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Flashcards in P5 - Space For Reflection Deck (398):
1

What happens if the distance from a planet is doubled (gravity)?

Gravitational force decreases by a factor of 4 (22)

2

What is the formula for gravity?

F ∝ 1/d²

3

What does gravity provide to ensure planets orbit in a circular motion?

A centripetal force - it is directed to the centre of the circle.

4

What happens if a planet is twice as close (gravity)?

Gravitational force increases by a factor of 4

5

What is speed?

How fast something's going

6

Why is velocity a more useful measure of motion?

Because it describes both the speed and direction

7

What is a scalar quantity?

A quantity like speed that has only a number

8

What are some examples of scalar quantities?

Speed Mass Temperature Time Length

9

What is a vector quantity?

A quantity like velocity that has a direction and a number

10

What are some examples of vector quantities?

Velocity Force Displacement Acceleration Momentum

11

What is relative speed?

How fast something is going relative to something else.

12

What will the relative speed be of a car going the same way as you?

The car will have a small speed relative to your car

13

What will the relative speed be of a car going the opposite direction to you?

The car will have a bigger speed relative to your car.

14

What happens to the vectors if two things are moving in the same directions?

The vectors are added

15

What happens to the vectors if two things are moving in the same directions?

Vectors are subtracted

16

What is used if an object mov against the current e.g. Across the wind?

Pythagoras theorem. Velocity is needed.

17

What does u stand for in the equations of motion?

Initial velocity

18

What does v stand for in the equations of motion?

Final velocity

19

What does s stand for in the equations of motion?

Distance (or displacement)

20

What does t stand for in the equations of motion?

Time

21

What does a stand for in the equations of motion?

Acceleration

22

What is a projectile?

Something that is projected, or dropped and only has Earth's gravitational field acting on it.

23

Give some examples of projectiles...

Golf ball, missile, football.

24

What is a trajectory?

The path a projectile takes

25

What shape is a projectile trajectory?

Parabolic

26

What does the distance a projectile travels depend on?

Angle it is launched at.

27

At what angle will a projectile travel the furthest?

45 degrees

28

What happens to the projectile if launched at less than 45 degrees?

Won't travel as far

29

What happens to the distance travelled by the projectile if launched at more than 45 degrees?

Projectile will take longer to hit ground and won't travel as far

30

How is motion split up?

Into horizontal and vertical

31

How does gravity affect motion?

Acts downwards - doesn't affect horizontal at all.

32

Why does an object launched horizontally accelerate vertically?

Due to gravity. Has no horizontal acceleration (velocity stays same).

33

How is the resultant velocity calculated?

The vector sum of the separate motions

34

What happens when an object exerts a force on another object?

It always experiences a force in return.

35

What is an interaction pair?

When an object exerts a force and experiences one in return

36

What is Newton's Third Law of Motion?

If object A exerts a force in object B, then object B exerts an equal and opposite force on object A.

37

What is the equation for momentum?

Mass x velocity

38

What are the units for momentum?

Kg m/s

39

In a collision when no other forces are involved, what happens to momentum?

It is conserved

40

What does coalesce mean?

Join together (when two objects collide)

41

What does m1 stand for?

Mass of first object

42

What does m2 stand for?

Mass of second object

43

What does u1 stand for?

Velocity of first object

44

What does u2 stand for?

Velocity of second object

45

What does v stand for in the momentum equation?

Velocity of combined objects

46

If the forces are equal how does anything move?

The forces are acting on different objects

47

What does kinetic theory say that gases consist of?

Very small particles constantly moving in random directions.

48

How much space do the gas particles take up?

Hardly any - most of gas is empty space.

49

What do the particles in a gas do with each other?

Constantly collide and bounce off each other (or off the walls).

50

Why do gas particles exert a force when they collide?

Because gas particles have some mass.

51

What happens with gas particles in a sealed container?

Gas particles smash against container walls - creates outward pressure.

52

What happens when the same volume of gas is put in a bigger container?

Larger volume decreases pressure. Fewer collisions between gas particles and walls.

53

What happens when the volume is reduced in a gas container?

Particles are more squashed - hit walls more often - pressure increase.

54

What does the pressure of a gas depend on?

How fast the particles are moving and how often they hit the container walls.

55

What happens if you heat a gas?

Particles move faster and have more kinetic energy. Hit container wall more often, creating more pressure.

56

What happens if a gas is cooled?

Particles have less kinetic energy - hit walls with less force and less often - pressure reduced.

57

As well as moving and having a mass, what else do gas particles have?

Momentum

58

What happens to momentum when gas particles hit the container walls?

Changes velocity and momentum - exerts force on container (pressure).

59

What is an orbit?

A balance between the forward motion of an object and a force pulling it inwards. (centripetal)

60

What provides the centripetal force so the planets orbit the Sun in orbits?

Gravitational force between each planet and the sun.

61

There must be a force acting on it if...

An object is travelling in a circle and constantly changing direction.

62

Why does the moon orbit the earth?

Because of the centripetal force produced by the gravitational force between Earth and Moon.

63

What happens to gravity the closer you get to a star or planet?

Stronger force of attraction

64

What does a stronger force of attraction mean the planets do?

Planets nearer sun move faster and cover orbits quicker.

65

In addition to planets/stars, what else are held in orbit by gravity?

Moons, artificial satellites and space stations.

66

What type of orbit do periodic comets have?

Highly elliptical orbits

67

What happens to comets when they are closer to the sun?

Greater the gravitational force of attraction. Travel much faster here.

68

What type of orbit do communications satellites need?

Quite high orbit. Above equator. Orbit once every 24hrs.

69

Whereabouts do communications satellites stay in relation to the earth?

Over same point. Earth rotates with them.

70

What is the name given to communications satellites?

Geostationary artificial satellites/geosynchronous satellites.

71

What are geostationary satellites ideal for?

Telephone, TV and radio.

72

Why are geostationary satellites ideal for TV, radio and telephone?

Stay at same point above Earth and can transfer signals from one side of earth to another in fraction of a second.

73

Why are geostationary satellites not used for weather and spying satellites?

Too high and too stationary

74

What kind of orbit do weather and spying satellites need?

Low polar orbit, passing over both poles.

75

What happens in a low polar orbit?

Satellite sweeps over both poles whilst earth rotates beneath it.

76

What is the difference for low polar orbit satellites in terms of gravity?

Much closer to earth = pull of gravity stronger and move faster.

77

How long is the orbit of a low polar orbit satellite?

Often under 2 hours

78

What happens each time the low polar orbit satellite orbits and what does this allow?

It can scan the next bit of globe and allows whole surface. To be monitored each day.

79

What wave do communications to and from satellites use?

Microwaves

80

How are signals for satellite TV and phones transmitted?

From transmitter. Picked up by satellite receiver dish orbiting 1000s of km above Earth. Satellite transmits signal back to earth in different direction and received by satellite dish on ground. OR satellites receiving signal retransmit it to other satellites and eventually back to earth.

81

What type of frequency do microwaves have?

High frequency - over 3,000MHz (3GHz)

82

How can microwaves reach distant parts of the planet?

They pass easily through the atmosphere to satellites orbiting Earth.

83

How is the frequency different for low orbit satellites than those in a geostationary orbit?

Those in low orbit use lower frequencies.

84

Why do satellite signals weaken?

They travel over long distances (losing intensity and picking up interference).

85

Why are digital signals used for satellites?

High quality and don't suffer as much interference.

86

What is the magnification formula?

image size ÷ object size

87

What type of lenses do magnifying glasses use to create images?

Convex lenses

88

Where must the object being magnified be placed?

Closer to the lens than the focal length

89

What image is produced from a magnifying glass?

Virtual image

90

What are the stages when photographing an object?

Light from object travels to camera and is refracted by lens, forming an image on the light sensor.

91

What is the image type when taking a photograph?

Real image - light rays actually meet

92

What is the image size when taking photos? Why?

Smaller than object because object's further away than focal length of lens

93

How does the image appear in a photo?

Inverted (upside down)

94

Where is an object positioned for a projector?

Object much closer than focal length

95

What size if the image from a projector?

Larger

96

How does the object need to be placed when projecting it?

Upside down and very close to lens

97

What happens to light when an object is projected?

Refracted by lens

98

What image is produced when an object is projected?

Real, inverted and magnified image on screen

99

When will an image be in focus?

When the light that forms the image converges on the screen or sensor

100

How is the image focused in cameras/projectors?

By moving the lens closer to or further from the object

101

The closer the object to the lens...

The further from the lens the image is formed

102

If 2 speakers both play the same note at exactly the same time where does constructive interference occur?

When distance travelled by waves from both speakers is either same or different by a WHOLE NUMBER of wavelengths.

103

If 2 speakers both play the same note at exactly the same time, where does destructive interference occur?

When difference in distance travelled by waves from both speakers is 1/2 wavelength, 1 1/2  wavelength, 2 1/2  wavelength, etc.

104

What is path difference?

Difference in distance travelled by waves from both speakers

105

What is a pattern of loud and quiet called?

Interference pattern

106

What is an interference pattern?

Pattern of constructive (loud) and destructive (quiet) interference. Applies for all type of waves.

107

What do you need to get a stable interference pattern?

A coherent wave source

108

What does it mean to have a coherent wave source?

  1. Waves at same frequency/wavelength
  2. Waves in phase (troughs and crests line up)
  3. Waves have same amplitude

109

What is the coherent source for light?

Monochromatic light (type produces interference patterns)

110

Why are EM waves with different frequencies used to transmit different types of communication signals?

Thay behave differently in the atmosphere

111

What happens to signals below 30MHz?

Radiowaves reflected off ionosphere, allowing wave to travel longer distances and deal with Earth's curvature.

112

What happens to signals between 30MHz and 30GHz?

Radiowaves and Microwaves pass straight through atmosphere so transmissions must be in line of sight (can't reflect off atmosphere).

113

What happens to signals above 30GHz?

Rain and dust in atmosphere absorb and scatter microwaves. This reduces signal strength, so highest frequency that can be used for satellite transmission is about 30GHz.

114

If 2 speakers both play the same note at exactly the same time, depending on where you stand, what do you hear?

Either loud sound or almost nothing

115

If 2 speakers both play the same note at exactly the same time what is heard in areas of constructive interference?

Loud sound - waves in phase and amplitude doubles

116

If 2 speakers both play the same note at exactly the same time what is heard in areas of destructive interference?

Almost no sound - waves exactly out of phase, cancel out.

117

What happens to all waves as they pass an object or through a narrow gap?

They diffract

118

What is classed as a 'narrow gap'?

One which is about the same size as the wavelength.

119

What achieves the maximum amount of diffraction?

When size of gap = wavelength of wave

120

Why are long-wave radiowaves great for broadcasting?

Can diffract over hills, through tunnels and over horizon.

121

How are terrestrial TV and radio signals transmitted?

Using radiowaves (and a dish) and are received by an aerial.

122

How is a narrow beam produced when transmitting microwaves or radiowaves?

Dishes are many times larger than wavelength so waves don't diffract much - producing a narrow beam.

123

What do all waves cause in a medium?

Some kind of disturbance.

124

What do water waves disturb?

Water particles

125

What do sound waves disturb?

Air particles

126

What do EM waves disturb?

Electric and Magnetic fields

127

What is constructive interference?

Waves disturb in the same direction and reinforce each other.

128

What is destructive interference?

Waves disturb in opposite directions and cancel each other out.

129

What is the total amplitude of a wave at any point?

The sum of the displacements (taking into account direction) of the wave at that point.

130

131

When do you get interference patterns?

When waves of equal frequency or wavelength overlap.

132

What happens when a wavefront passes through a gap?

Light from each point along the gap diffracts.

133

What must a gap be so that light will diffract?

About the same size as the wavelength of light.

134

What does an interference pattern create?

A bright central fringe, with alternating dark and bright fringes on either side.

135

What 2 theories were there in the 17th Century to explain the nature of light?

  • Particle theory - Isaac Newton
  • Wave theory - Christiaan Huygens

136

What could the particle theory explain?

Reflection and refraction

137

What could the particle theory not explain?

Diffraction and interference

138

Why could the particle theory not explain diffraction and interference?

They are both unique to waves

139

What did Thomas Young's double slit experiment show?

That light could diffract (through 2 narrow slits) and interfere (to form interference patterns on screen).

140

What did Thomas Young's Double Slit experiment involve?

A coherent light source (e.g. laser) shone through two narrow slits.

141

What is now accepted about light?

It shows properties of a wave (diffraction, interference and polarisation).

142

What type of wave are EM waves?

Transverse - vibrations at 90º to direction of travel.

143

How can you make (imitate) a transverse wave?

Shake a rope up and down/side to side, or in a mixture of directions.

144

What is plane polarisation?

Filtering out all vibrations of waves except a particular direction.

145

What is ordinary light a mixture of?

Vibrations in different directions

146

What does passing light through a polarising filter do?

Filter only transmits vibrations in one particular direction.

147

What is plane polarised light made up of?

Vibrations in one direction only

148

What happens when light is reflected from some surfaces like water?

It is partly plane polarised

149

What do polaroid sunglasses act as?

Polarising filters - can filter out reflected glare from sea/snow

150

What is refraction?

When waves change direction as they enter a different medium

151

What causes refraction?

Change of speed in waves which causes change in wavelength - NO CHANGE IN FREQ

152

What happens when a wave passes the boundary between 2 substances?

Changes speed

153

How does the wave refract if the wave speed decreases?

Wave bends towards normal

154

How does the wave refract when the wave speed increases?

Wave bends away from the normal.

155

What does light slow down to when it enters glass?

2/3 normal speed in air (about 2x108m/s rather than 3 x 108m/s)

156

What is refractive index?

Ratio of speed of light in a vacuum to the speed of light in a medium.

157

What is the refractive index basically a measure of?

The amount of bending

158

The higher the refractive index...

The more the light bends when it enters/leaves the medium.

159

What happens when waves hit a boundary along the normal (exactly 90º)?

No change in direction - change in speed and wavelength

160

How is the absolute refractive index of a material defined?

speed of light (c) ÷ speed of light in medium (v)

161

What is the refractive index of glass and why?

High (around 1.5) - light slows down a lot in glass

162

What is the refractive index of water compared to glass?

Lower (around 1.33) - light slows down less in water than in glass.

163

What is the refractive index of air?

About same as in a vacuum - 1.

164

Why are different colours of light refracted by different amounts?

They travel at different speeds in any given medium (but same in a vacuum).

165

Which colour of light slows down the least?

Red - refracted least and has lowest refractive index (1.514...)

166

What colour of light is refracted most?

Blue - higher refractive index (1.523...)

167

What is used to make different colours of light emerge at different angles?

A prism

168

What can a prism do to light?

Make different colours of white light refract, producing a spectrum - dispersion.

169

What is dispersion?

When a spectrum is produced to show colours of rainbow.

170

When does TIR only happen?

When light travels from a more dense medium with a higher RI to a less dense medium with a lower RI.

 

E.g. Glass to water

171

What is TIR?

When angle of incidence is greater than critical angle, ray of light won't come out but is reflected back into medium.

172

What happens when angle of incidence is less than critical angle?

Most light passes through into air but little bit is internally reflected.

173

What happens when angle of incidence is equal to critical angle?

Emerging ray travels along the surface. Quite a bit internal reflection.

174

What happens when angle of incidence is greater than critical angle?

No light comes out - all totally internally reflected

175

Different media have different critical angles so the higher the refractive index of the medium....

The lower the critical angle will be.

176

What is the critical angle for glass?

About 42º

177

Why is a critical angle of 42 useful in glass?

45º can be used to get TIR e.g. optical fibres

178

What can TIR be used in?

Optical fibres, prisms in binoculars, reflectors, road signs and cat's eyes.

179

What is a real image?

Where light rays from an object come together to form an image on a screen (inc. retina - eye's screen).

180

What can you do to real images?

Project them onto a screen

181

What is a virtual image?

When rays diverge so light from object appears to come from a different place.

182

What can't you do with a virtual image?

Project it onto a screen

183

What type of image is looking in a mirror?

Virtual - object (face) appears behind mirror.

184

What is the image when you look through a magnfiying glass?

Virtual - appears bigger and further away than it actually is.

185

What 4 things describe an image?

  1. How big compared to original
  2. Real or virtual
  3. Upright or inverted
  4. Where it is (in relation to lens and focal point)

186

What shape is a converging lens?

Convex

187

What does a convex lens do to light?

Rays converge to a focus

188

What happens if the rays entering the lens are parallel to each other and to the principal axis?

Focuses them at a point - focal point

189

What is the focal length?

Distance between centre of lens and focal point

190

What happens to the speed of a ray travelling parallel to the principal axis?

Slows down upon entry and bends towards normal.

191

What happens to a ray travelling parallel to the principal axis when it hits the 'glass to air' boundary?

Speeds up - bends away from normal

192

When a ray is travelling parallel to the principal axis, what does the curvature of the lens mean?

All the rays hitting different parts of lens are bent towards some focal point to form image.

193

What does a ray passing through the optical centre of the lens appear to do?

Pass straight through

194

How does a ray passing through the optical centre of the lens exit?

At same angle as entry but on opposite side to principal axis, so bent same amount - opposite direction.

195

Describe how a convex lens can work in the opposite way...

Turns diverging rays into parallel light

196

What type of image can convex lenses produce?

Real or virtual depending on how close object is to lens

197

What will an object at 2F produce?

Real, inverted image, same size as object and at 2F

198

What will an object between F and 2F produce?

Real, inverted image bigger than object and beyond 2F

199

What will an object nearer than F produce?

Virtual image, right way up, bigger than object and on same side of lens.

200

Gravitational force decreases by a factor of 4 (22)

What happens if the distance from a planet is doubled (gravity)?

201

F ∝ 1/d²

What is the formula for gravity?

202

A centripetal force - it is directed to the centre of the circle.

What does gravity provide to ensure planets orbit in a circular motion?

203

Gravitational force increases by a factor of 4

What happens if a planet is twice as close (gravity)?

204

How fast something's going

What is speed?

205

Because it describes both the speed and direction

Why is velocity a more useful measure of motion?

206

A quantity like speed that has only a number

What is a scalar quantity?

207

Speed Mass Temperature Time Length

What are some examples of scalar quantities?

208

A quantity like velocity that has a direction and a number

What is a vector quantity?

209

Velocity Force Displacement Acceleration Momentum

What are some examples of vector quantities?

210

How fast something is going relative to something else.

What is relative speed?

211

The car will have a small speed relative to your car

What will the relative speed be of a car going the same way as you?

212

The car will have a bigger speed relative to your car.

What will the relative speed be of a car going the opposite direction to you?

213

The vectors are added

What happens to the vectors if two things are moving in the same directions?

214

Vectors are subtracted

What happens to the vectors if two things are moving in the same directions?

215

Pythagoras theorem. Velocity is needed.

What is used if an object mov against the current e.g. Across the wind?

216

Initial velocity

What does u stand for in the equations of motion?

217

Final velocity

What does v stand for in the equations of motion?

218

Distance (or displacement)

What does s stand for in the equations of motion?

219

Time

What does t stand for in the equations of motion?

220

Acceleration

What does a stand for in the equations of motion?

221

Something that is projected, or dropped and only has Earth's gravitational field acting on it.

What is a projectile?

222

Golf ball, missile, football.

Give some examples of projectiles...

223

The path a projectile takes

What is a trajectory?

224

Parabolic

What shape is a projectile trajectory?

225

Angle it is launched at.

What does the distance a projectile travels depend on?

226

45 degrees

At what angle will a projectile travel the furthest?

227

Won't travel as far

What happens to the projectile if launched at less than 45 degrees?

228

Projectile will take longer to hit ground and won't travel as far

What happens to the distance travelled by the projectile if launched at more than 45 degrees?

229

Into horizontal and vertical

How is motion split up?

230

Acts downwards - doesn't affect horizontal at all.

How does gravity affect motion?

231

Due to gravity. Has no horizontal acceleration (velocity stays same).

Why does an object launched horizontally accelerate vertically?

232

The vector sum of the separate motions

How is the resultant velocity calculated?

233

It always experiences a force in return.

What happens when an object exerts a force on another object?

234

When an object exerts a force and experiences one in return

What is an interaction pair?

235

If object A exerts a force in object B, then object B exerts an equal and opposite force on object A.

What is Newton's Third Law of Motion?

236

Mass x velocity

What is the equation for momentum?

237

Kg m/s

What are the units for momentum?

238

It is conserved

In a collision when no other forces are involved, what happens to momentum?

239

Join together (when two objects collide)

What does coalesce mean?

240

Mass of first object

What does m1 stand for?

241

Mass of second object

What does m2 stand for?

242

Velocity of first object

What does u1 stand for?

243

Velocity of second object

What does u2 stand for?

244

Velocity of combined objects

What does v stand for in the momentum equation?

245

The forces are acting on different objects

If the forces are equal how does anything move?

246

Very small particles constantly moving in random directions.

What does kinetic theory say that gases consist of?

247

Hardly any - most of gas is empty space.

How much space do the gas particles take up?

248

Constantly collide and bounce off each other (or off the walls).

What do the particles in a gas do with each other?

249

Because gas particles have some mass.

Why do gas particles exert a force when they collide?

250

Gas particles smash against container walls - creates outward pressure.

What happens with gas particles in a sealed container?

251

Larger volume decreases pressure. Fewer collisions between gas particles and walls.

What happens when the same volume of gas is put in a bigger container?

252

Particles are more squashed - hit walls more often - pressure increase.

What happens when the volume is reduced in a gas container?

253

How fast the particles are moving and how often they hit the container walls.

What does the pressure of a gas depend on?

254

Particles move faster and have more kinetic energy. Hit container wall more often, creating more pressure.

What happens if you heat a gas?

255

Particles have less kinetic energy - hit walls with less force and less often - pressure reduced.

What happens if a gas is cooled?

256

Momentum

As well as moving and having a mass, what else do gas particles have?

257

Changes velocity and momentum - exerts force on container (pressure).

What happens to momentum when gas particles hit the container walls?

258

A balance between the forward motion of an object and a force pulling it inwards. (centripetal)

What is an orbit?

259

Gravitational force between each planet and the sun.

What provides the centripetal force so the planets orbit the Sun in orbits?

260

An object is travelling in a circle and constantly changing direction.

There must be a force acting on it if...

261

Because of the centripetal force produced by the gravitational force between Earth and Moon.

Why does the moon orbit the earth?

262

Stronger force of attraction

What happens to gravity the closer you get to a star or planet?

263

Planets nearer sun move faster and cover orbits quicker.

What does a stronger force of attraction mean the planets do?

264

Moons, artificial satellites and space stations.

In addition to planets/stars, what else are held in orbit by gravity?

265

Highly elliptical orbits

What type of orbit do periodic comets have?

266

Greater the gravitational force of attraction. Travel much faster here.

What happens to comets when they are closer to the sun?

267

Quite high orbit. Above equator. Orbit once every 24hrs.

What type of orbit do communications satellites need?

268

Over same point. Earth rotates with them.

Whereabouts do communications satellites stay in relation to the earth?

269

Geostationary artificial satellites/geosynchronous satellites.

What is the name given to communications satellites?

270

Telephone, TV and radio.

What are geostationary satellites ideal for?

271

Stay at same point above Earth and can transfer signals from one side of earth to another in fraction of a second.

Why are geostationary satellites ideal for TV, radio and telephone?

272

Too high and too stationary

Why are geostationary satellites not used for weather and spying satellites?

273

Low polar orbit, passing over both poles.

What kind of orbit do weather and spying satellites need?

274

Satellite sweeps over both poles whilst earth rotates beneath it.

What happens in a low polar orbit?

275

Much closer to earth = pull of gravity stronger and move faster.

What is the difference for low polar orbit satellites in terms of gravity?

276

Often under 2 hours

How long is the orbit of a low polar orbit satellite?

277

It can scan the next bit of globe and allows whole surface. To be monitored each day.

What happens each time the low polar orbit satellite orbits and what does this allow?

278

Microwaves

What wave do communications to and from satellites use?

279

From transmitter. Picked up by satellite receiver dish orbiting 1000s of km above Earth. Satellite transmits signal back to earth in different direction and received by satellite dish on ground. OR satellites receiving signal retransmit it to other satellites and eventually back to earth.

How are signals for satellite TV and phones transmitted?

280

High frequency - over 3,000MHz (3GHz)

What type of frequency do microwaves have?

281

They pass easily through the atmosphere to satellites orbiting Earth.

How can microwaves reach distant parts of the planet?

282

Those in low orbit use lower frequencies.

How is the frequency different for low orbit satellites than those in a geostationary orbit?

283

They travel over long distances (losing intensity and picking up interference).

Why do satellite signals weaken?

284

High quality and don't suffer as much interference.

Why are digital signals used for satellites?

285

image size ÷ object size

What is the magnification formula?

286

Convex lenses

What type of lenses do magnifying glasses use to create images?

287

Closer to the lens than the focal length

Where must the object being magnified be placed?

288

Virtual image

What image is produced from a magnifying glass?

289

Light from object travels to camera and is refracted by lens, forming an image on the light sensor.

What are the stages when photographing an object?

290

Real image - light rays actually meet

What is the image type when taking a photograph?

291

Smaller than object because object's further away than focal length of lens

What is the image size when taking photos? Why?

292

Inverted (upside down)

How does the image appear in a photo?

293

Object much closer than focal length

Where is an object positioned for a projector?

294

Larger

What size if the image from a projector?

295

Upside down and very close to lens

How does the object need to be placed when projecting it?

296

Refracted by lens

What happens to light when an object is projected?

297

Real, inverted and magnified image on screen

What image is produced when an object is projected?

298

When the light that forms the image converges on the screen or sensor

When will an image be in focus?

299

By moving the lens closer to or further from the object

How is the image focused in cameras/projectors?

300

The further from the lens the image is formed

The closer the object to the lens...

301

When distance travelled by waves from both speakers is either same or different by a WHOLE NUMBER of wavelengths.

If 2 speakers both play the same note at exactly the same time where does constructive interference occur?

302

When difference in distance travelled by waves from both speakers is 1/2 wavelength, 1 1/2  wavelength, 2 1/2  wavelength, etc.

If 2 speakers both play the same note at exactly the same time, where does destructive interference occur?

303

Difference in distance travelled by waves from both speakers

What is path difference?

304

Interference pattern

What is a pattern of loud and quiet called?

305

Pattern of constructive (loud) and destructive (quiet) interference. Applies for all type of waves.

What is an interference pattern?

306

A coherent wave source

What do you need to get a stable interference pattern?

307

  1. Waves at same frequency/wavelength
  2. Waves in phase (troughs and crests line up)
  3. Waves have same amplitude

What does it mean to have a coherent wave source?

308

Monochromatic light (type produces interference patterns)

What is the coherent source for light?

309

Thay behave differently in the atmosphere

Why are EM waves with different frequencies used to transmit different types of communication signals?

310

Radiowaves reflected off ionosphere, allowing wave to travel longer distances and deal with Earth's curvature.

What happens to signals below 30MHz?

311

Radiowaves and Microwaves pass straight through atmosphere so transmissions must be in line of sight (can't reflect off atmosphere).

What happens to signals between 30MHz and 30GHz?

312

Rain and dust in atmosphere absorb and scatter microwaves. This reduces signal strength, so highest frequency that can be used for satellite transmission is about 30GHz.

What happens to signals above 30GHz?

313

Either loud sound or almost nothing

If 2 speakers both play the same note at exactly the same time, depending on where you stand, what do you hear?

314

Loud sound - waves in phase and amplitude doubles

If 2 speakers both play the same note at exactly the same time what is heard in areas of constructive interference?

315

Almost no sound - waves exactly out of phase, cancel out.

If 2 speakers both play the same note at exactly the same time what is heard in areas of destructive interference?

316

They diffract

What happens to all waves as they pass an object or through a narrow gap?

317

One which is about the same size as the wavelength.

What is classed as a 'narrow gap'?

318

When size of gap = wavelength of wave

What achieves the maximum amount of diffraction?

319

Can diffract over hills, through tunnels and over horizon.

Why are long-wave radiowaves great for broadcasting?

320

Using radiowaves (and a dish) and are received by an aerial.

How are terrestrial TV and radio signals transmitted?

321

Dishes are many times larger than wavelength so waves don't diffract much - producing a narrow beam.

How is a narrow beam produced when transmitting microwaves or radiowaves?

322

Some kind of disturbance.

What do all waves cause in a medium?

323

Water particles

What do water waves disturb?

324

Air particles

What do sound waves disturb?

325

Electric and Magnetic fields

What do EM waves disturb?

326

Waves disturb in the same direction and reinforce each other.

What is constructive interference?

327

Waves disturb in opposite directions and cancel each other out.

What is destructive interference?

328

The sum of the displacements (taking into account direction) of the wave at that point.

What is the total amplitude of a wave at any point?

329

330

When waves of equal frequency or wavelength overlap.

When do you get interference patterns?

331

Light from each point along the gap diffracts.

What happens when a wavefront passes through a gap?

332

About the same size as the wavelength of light.

What must a gap be so that light will diffract?

333

A bright central fringe, with alternating dark and bright fringes on either side.

What does an interference pattern create?

334

  • Particle theory - Isaac Newton
  • Wave theory - Christiaan Huygens

What 2 theories were there in the 17th Century to explain the nature of light?

335

Reflection and refraction

What could the particle theory explain?

336

Diffraction and interference

What could the particle theory not explain?

337

They are both unique to waves

Why could the particle theory not explain diffraction and interference?

338

That light could diffract (through 2 narrow slits) and interfere (to form interference patterns on screen).

What did Thomas Young's double slit experiment show?

339

A coherent light source (e.g. laser) shone through two narrow slits.

What did Thomas Young's Double Slit experiment involve?

340

It shows properties of a wave (diffraction, interference and polarisation).

What is now accepted about light?

341

Transverse - vibrations at 90º to direction of travel.

What type of wave are EM waves?

342

Shake a rope up and down/side to side, or in a mixture of directions.

How can you make (imitate) a transverse wave?

343

Filtering out all vibrations of waves except a particular direction.

What is plane polarisation?

344

Vibrations in different directions

What is ordinary light a mixture of?

345

Filter only transmits vibrations in one particular direction.

What does passing light through a polarising filter do?

346

Vibrations in one direction only

What is plane polarised light made up of?

347

It is partly plane polarised

What happens when light is reflected from some surfaces like water?

348

Polarising filters - can filter out reflected glare from sea/snow

What do polaroid sunglasses act as?

349

When waves change direction as they enter a different medium

What is refraction?

350

Change of speed in waves which causes change in wavelength - NO CHANGE IN FREQ

What causes refraction?

351

Changes speed

What happens when a wave passes the boundary between 2 substances?

352

Wave bends towards normal

How does the wave refract if the wave speed decreases?

353

Wave bends away from the normal.

How does the wave refract when the wave speed increases?

354

2/3 normal speed in air (about 2x108m/s rather than 3 x 108m/s)

What does light slow down to when it enters glass?

355

Ratio of speed of light in a vacuum to the speed of light in a medium.

What is refractive index?

356

The amount of bending

What is the refractive index basically a measure of?

357

The more the light bends when it enters/leaves the medium.

The higher the refractive index...

358

No change in direction - change in speed and wavelength

What happens when waves hit a boundary along the normal (exactly 90º)?

359

speed of light (c) ÷ speed of light in medium (v)

How is the absolute refractive index of a material defined?

360

High (around 1.5) - light slows down a lot in glass

What is the refractive index of glass and why?

361

Lower (around 1.33) - light slows down less in water than in glass.

What is the refractive index of water compared to glass?

362

About same as in a vacuum - 1.

What is the refractive index of air?

363

They travel at different speeds in any given medium (but same in a vacuum).

Why are different colours of light refracted by different amounts?

364

Red - refracted least and has lowest refractive index (1.514...)

Which colour of light slows down the least?

365

Blue - higher refractive index (1.523...)

What colour of light is refracted most?

366

A prism

What is used to make different colours of light emerge at different angles?

367

Make different colours of white light refract, producing a spectrum - dispersion.

What can a prism do to light?

368

When a spectrum is produced to show colours of rainbow.

What is dispersion?

369

When light travels from a more dense medium with a higher RI to a less dense medium with a lower RI.

 

E.g. Glass to water

When does TIR only happen?

370

When angle of incidence is greater than critical angle, ray of light won't come out but is reflected back into medium.

What is TIR?

371

Most light passes through into air but little bit is internally reflected.

What happens when angle of incidence is less than critical angle?

372

Emerging ray travels along the surface. Quite a bit internal reflection.

What happens when angle of incidence is equal to critical angle?

373

No light comes out - all totally internally reflected

What happens when angle of incidence is greater than critical angle?

374

The lower the critical angle will be.

Different media have different critical angles so the higher the refractive index of the medium....

375

About 42º

What is the critical angle for glass?

376

45º can be used to get TIR e.g. optical fibres

Why is a critical angle of 42 useful in glass?

377

Optical fibres, prisms in binoculars, reflectors, road signs and cat's eyes.

What can TIR be used in?

378

Where light rays from an object come together to form an image on a screen (inc. retina - eye's screen).

What is a real image?

379

Project them onto a screen

What can you do to real images?

380

When rays diverge so light from object appears to come from a different place.

What is a virtual image?

381

Project it onto a screen

What can't you do with a virtual image?

382

Virtual - object (face) appears behind mirror.

What type of image is looking in a mirror?

383

Virtual - appears bigger and further away than it actually is.

What is the image when you look through a magnfiying glass?

384

  1. How big compared to original
  2. Real or virtual
  3. Upright or inverted
  4. Where it is (in relation to lens and focal point)

What 4 things describe an image?

385

Convex

What shape is a converging lens?

386

Rays converge to a focus

What does a convex lens do to light?

387

Focuses them at a point - focal point

What happens if the rays entering the lens are parallel to each other and to the principal axis?

388

Distance between centre of lens and focal point

What is the focal length?

389

Slows down upon entry and bends towards normal.

What happens to the speed of a ray travelling parallel to the principal axis?

390

Speeds up - bends away from normal

What happens to a ray travelling parallel to the principal axis when it hits the 'glass to air' boundary?

391

All the rays hitting different parts of lens are bent towards some focal point to form image.

When a ray is travelling parallel to the principal axis, what does the curvature of the lens mean?

392

Pass straight through

What does a ray passing through the optical centre of the lens appear to do?

393

At same angle as entry but on opposite side to principal axis, so bent same amount - opposite direction.

How does a ray passing through the optical centre of the lens exit?

394

Turns diverging rays into parallel light

Describe how a convex lens can work in the opposite way...

395

Real or virtual depending on how close object is to lens

What type of image can convex lenses produce?

396

Real, inverted image, same size as object and at 2F

What will an object at 2F produce?

397

Real, inverted image bigger than object and beyond 2F

What will an object between F and 2F produce?

398

Virtual image, right way up, bigger than object and on same side of lens.

What will an object nearer than F produce?