Physics Waves March 2019

Question 1

What are the two types of waves?

Answer 1

Longitudinal and Transverse.

Question 2

What happens in longitudinal waves?

Answer 2

• The vibrations that cause the wave are parallel to the energy transfer.
• It needs a material to travel in e.g. air.
• Squashed sections are called compressions.
• Stretched sections are called rarefactions.

Question 3

What happens in transverse waves?

Answer 3

• The vibrations that cause the wave are at right-angles to the energy transfer.
• Doesn’t need a material to travel in.

Question 4

What waves are transverse or longitudinal or both?

Answer 4

Transverse = Water and any electromagnetic wave.
Longitudinal = Sound waves.
Both = Seismic/shock waves.

Question 5

What are the wave characteristics?

Answer 5

Amplitude, wavelength, peak/trough, frequency, period and wave speed.

Question 6

What is frequency?

Answer 6

The number of waves made every second.
f = # of waves/time (s)
Hz - Hertz

Question 7

What is amplitude?

Answer 7

The distance from zero/rest position to a peak or trough.

m - Meters

Question 8

What is wavelength?

Answer 8

The distance from two peaks or troughs.

m - Meters

Question 9

What is a period?

Answer 9

The time it takes to produce a wave.
Time = 1/frequency
s - Seconds

Question 10

What is wave speed?

Answer 10

How far the energy in a wave is transferred in a certain time.
Velocity = frequency x wavelength v = fλ
m/s - Meters per Second

Question 11

What are peaks and troughs?

Answer 11

Peak - The highest point of the wave (transverse) or the centre of the compression (longitudinal).

Trough - The lowest point of the wave (transverse) or the centre of the rarefaction (longitudinal).

Question 12

What are the characteristics of reflected light?

Answer 12

Normal = Imaginary line 90 degrees to surface.
Incident ray = The wave before being reflected.
Reflected ray = The wave after being reflected.
Angle of incidence = Angle of which the incident ray hit the surface (should = angle of reflection).
Angle of reflection = Angle of which the reflected ray was reflected (should = angle of incidence).

Question 13

What is diffuse reflection?

Answer 13

When both the angle of incidence and reflection are the same (for multiple waves) but the direction of the rays are not the same.
Caused when the surface isn’t flat/smooth.

Question 14

What are real and virtual images?

Answer 14

Real - You can see the image on a piece of paper.

Virtual - You cannot see the image.

Question 15

What do magnified and reduced mean?

Answer 15

Magnified - The image is bigger than the object.

Reduced - The image is smaller than the object.

Question 16

How do you find the virtual image from a mirror on a ray diagram?

Answer 16

Draw two lines form the object to the mirror (at different angles), then draw two lines from those points to either edge of the eye. Extend the lines through the mirror: Where they connect is the spot of the virtual image. It should be the same distance from the mirror as the object.

Question 17

What is refraction?

Answer 17

Refraction is the change in direction of light when the speed changes (speed changes due to the density of the material it travels through).

Question 18

What happens when light travels into a more/less dense object?

Answer 18

More dense - When light travels from a less dense object to a more dense object (air to glass) it bends towards the normal (AoI is bigger than AoR). This is because the wave speed and wavelength increase.

Less dense - When light travels from a more dense object to a less dense object (glass to air) it bends towards the normal (AoR is bigger than AoI). This is because the wave speed and wavelength decrease.

Question 19

How is refraction linked to water waves?

Answer 19

When going from shallow to deep the wave speed and wavelength increase where as, going from deep to shallow the wave speed and wavelength decrease.

Same as refraction of light (deep = more dense, shallow = less dense).

Question 20

What are electromagnetic waves?

Answer 20

• Transverse waves.
• Transfer energy from one location to another.
• Not individual waves.
• Form part of a continuous spectrum.
• The waves have different names based on their frequency and wavelength.
• The waves have different effects and uses.

Question 21

What are the different properties of electromagnetic waves?

Answer 21

• They are transverse waves.
• They obey the wave equation. v = f x λ.
• Travel at the same speed in a vacuum (3 x 10^8 m/s).
• Can be reflected and refracted.

Question 22

What are the different electromagnetic waves?

Answer 22

(High frequency, short wavelength)
Gamma Rays
X-Rays
Ultraviolet
Visible light
Infrared
Microwaves
Radiowaves
(Low frequency, long wavelength)

Question 23

What are the two types of lenses?

Answer 23

Convex - Converging lens, bends outwards. (symbol is double sided arrow).

Concave - Diverging lens, bends inwards. (symbol is two armless and headless stick men with one upside down on the other).

Question 24

What is the focus and the focal length?

Answer 24

Focus - Point where light refracts to.

Focal length - Distance from focus and centre of lens.

Question 25

Is the image created on a convex or concave lens real of virtual?

Answer 25

Convex - Real as image can be seen on paper. (Appears in front of the object).

Concave - Virtual as image cannot be seen. (Appears behind the object).

Question 26

How can the focus and focal length be changed?

Answer 26

• Change the curvature of the lens.

- Change the optical density (material).

Question 27

What two/three lines should be drawn for convex ray diagrams when the object is outside the focus?

Answer 27

• A line perpendicular to the object and lens which refracts through the focus.
• A line going straight through the centre of the lens.
• A checking line that goes through the focus on the side of the object then goes perpendicular to the lens. (Opposite to first line).

Question 28

What two lines should be drawn for convex ray diagrams when the object is inside the focus?

Answer 28

• A line perpendicular to the object and lens which refracts through the focus.
• A line going straight through the centre of the lens.

To find the image, the lines should be extended backwards until they meet.

Question 29

What two lines should be drawn for concave ray diagrams no matter the position of the object?

Answer 29

• A line perpendicular to the object and lens which refracts away from the focus. This line should be extended backwards until it reaches the other line.
• A line going straight through the centre of the lens.

Question 30

What is the equation for magnification?

Answer 30

Magnification = image height / object height.

Question 31

What do filters do?

Answer 31

Filters absorb every colour except the colour they are. This means when white light passes through a blue filter the light becomes blue. When blue light goes through a blue filter the light is still blue. When red/green light goes through a blue filter no light goes through.