Physics topic 6

Question 1

What is the frequency of a wave?

Answer 1

The number of complete waves to pass a point in one second, its measured in HZ (hurtz).

Question 2

What is the period of a wave?
Include the equation

Answer 2

The amount of time it takes for a full cycle of the wave. Period (time) = 1 divided by the frequency (hz)

Question 3

What are the six main parts of a wave?

Answer 3

Amplitude (maximum displacement), wavelength (length of one full wave), crest (top of a wave), trough (bottom of a wave), undisturbed position (the full distance on the graph)

Question 4

What is a transverse wave?
Give examples

Answer 4

When the oscillations are perpendicular (90 degrees) to the direction of energy transfer.
Eg. All electromagnetic waves (light), ripples and waves in water, and waves on a string.

Question 5

What is a longitudinal wave?
Give examples

Answer 5

The oscillations are parallel to direction of energy transfer, for example, sound waves in air or waves in a spring.

Question 6

What is the equation for wave speed?

Answer 6

Wave speed (m/s) = frequency (hz) x wavelength (m)

Question 7

What is the purpose of an oscilloscope?

Answer 7

Gives you a visual image of a sound wave as a transverse wave. From that you can measure wavelength and frequency, so you can calculate wave speed.

Question 8

Briefly explain the aim of the ripple tank RP?

Answer 8

Using a dipper (powered by a signal generator), the aim is to measure the amount of waves per second, from the reflection on paper.

Question 9

Briefly explain the aim of the waves on a string RP?

Answer 9

Adjusting the frequency you will need to measure the wavelengths of the waves on a string, the best way to do this is to measure the lengths of four or five wavelengths and then divide by that number. Finally, you’ll calculate the speed of the wave.

Question 10

What are the three things that happen when a wave meets a boundary?

Answer 10

The wave is:
Absorbed, transmitted, reflected.

Question 11

What is an electromagnetic wave?

Answer 11

• transverse waves
• transfer energy from source to absorber
• they travel at the same speed as air through a vacuum (as they are vibrations of electric + magnetic fields)
• they travel at different speeds in different materials (can lead to refraction)
• can vary in wavelength
• there is a spectrum of different types of em wave

Question 12

What is the acronym for em waves?

Answer 12

Robots (radio waves)
Made (microwaves)
In (infrared)
Vietnam (visible light)
Use (ultraviolet)
X-ray (x rays)
Glasses (gamma rays)

Question 13

What does ionising mean?

Answer 13

As the waves get smaller, they can get into cells and damage them, starting at the beginning of the acronym is the most ionsing em wave.

Question 14

What are the properties of electromagnetic waves?

Answer 14

Electromagnetic waves travel at 3. 0×10 to the power of 3 m/s. They are transverse waves, so they move in the direction of right angles to the way in which the particles are vibrating. Electromagnetic waves can travel through a vacuum.

Question 15

What is the equation for wave speed?

Answer 15

Wave speed = frequency x wavelength

Question 16

uses of radio waves?

Answer 16

THEY’RE USED FOR COMMUNICATION
Em radiation no longer than 10cm.
Long wave radio signals (10km) can be transmitted around the world, as they are long wavelengths can bend.
Short wave signals (10-100m), Cana Lao be received from long distances as they are reflected from the ionosphere. (Bluetooth use this, and wireless headphones, and TV).

Question 17

What are microwaves used for?

Answer 17

• COMMUNICATION, such as to and from satellites, as they can easily pass through the earths watery atmosphere. (Transmitted to space and back to earth in a dif direction).
  -MICROWAVE OVENS, the micro-waves are absorbed by water molecules in food. The microwaves penetrate into the food (a few cm), before being absorbed and transferring 8th heat energy.

Question 18

What is refraction?

Answer 18

• refraction on my works when the ray is at an ANGLE.
  -When a wave changes direction at a boundary, it changes speed, and slows down.
  -If the wave is travelling along the normal (90 degree angle) it will change speed, but isn’t refracted.
• If the wave hits the boundary, at an angle it changes direction and is refracted.
• the amount of re fractions is dependant on its Angle and speed.
• the optical density of a material is how quickly light can travel through it.
• the wavelength changes once refracted but frequency stays the same.

Question 19

What are ray diagrams?

Answer 19

Rays are straight lines, that are perpendicular to wave fronts, and show the direction a wave is travelling in. (You can construct a ray diagram with a refracted waves)
1) draw the boundary between your two materials and the normal.
2) draw an incident ray that meets the normal at a boundary.
3) the angle between the incidence ray and normal is the angle of incidence, the angle between the refracted ray and the normal, is the refraction.
4) if the second material is optically denser than the first, then the refracted wave bends towards the normal and the angle of refraction is ambler than the incidence.

Question 20

What is a wave front diagram?

Answer 20

• a line which shows all the points on a wave that are the same position as each other, after a given number of wavelengths.
• when a wave crosses a boundary at an angle, only the part of a wave front crosses the boundary at first. If it’s travelling into a denser material, that part travels slower than the rest of the wave front.
  -by the time the whole wave crosses the boundary, the faster part will have travelled further than the slower part.
• this difference in distance travelled causes the wave to bend. (Refract)

Question 21

How are radio waves used for oscillating charges?

Answer 21

• made by oscillating waves, and magnetic fields.
• alternating currents are made up of these charges.
• you can produce these waves using an alternating current in an electrical circuit. This object used to create then is called a transmitter)
• once the transmitted waves reach a receiver, they’ll be absorbed.
• the energy carried by the wave sis transferred to the electrons.
• this energy causes the electrons to oscillate producing a current.

Question 22

What is infrared radiation used for?

Answer 22

Given out by all objects, the hotter it is, the more radiation it emits. IR cameras convert electrical signals into pictures to show the amount of IR being emitted. Absorbing this radiation causes an object to get hotter so can be used for FOOD, OR ELECTRIC HEATERS.

Question 23

What are fibre optic cables used for?

Answer 23

USED FOR VISIBLE LIGHT TO TRANSMIT DATA.
they are thin glass or plastic fibres which carry data over long distances as pulses of visible light. They work due to reflection, the light rays are bounced back and forth until they reach the end of the fibre. Visible light is used in these as it’s easy to refract light enough to remain in a narrow fibre. Light isn’t easily absorbed or scattered as it travels along a fibre.

Question 24

What is ultraviolet radiation?
And what is it used for?

Answer 24

This type of radiation contains fluorescence, and so absorbs radiation but emits bright fluorescent light. All fluorescent lights generate UV radiation which is absorbed and re emitted as visible light by a layer of phosphor inside the bulb (they’re energy efficient so good for long periods). Security pens use this uv light to glow, so good for the police.
Ultraviolet radiation is also used for tanning studios as it emits UV light.

Question 25

What are x-rays and gamma rays used for?

Answer 25

Radiographers use to take x-ray photographs, as x-rays pass easily through flesh but not so easily as through denser material such as bones. (It’s the amount of radiation absorbed which gives you the x-ray image). These rays also treat cancer (radiotherapy) as high doses of these rays kill al living cells (can be carefully directed towards cancerous ones). Gamma radiation can be used as a medical tracer - where the gamma emitting source is injected into the patient. Both types of rays can be harmful.

Question 26

What is the melting wax trick?

Answer 26

USED TO investigate absorption. The amount of infrared radiation absorbed by different materials depends on the material. 1) two ball bearings are each stuck to one side of s metal plate with solid pieces of candle wax, the other sides of the plate are facing the flame. 2) the sides of the plate that are facing towards the flame, each have a different surface colour, one Matt black the other silver. 3) the bearing on the black plate will fall first because it absorbs more infrared radiation - transferring more energy to the thermal store of the wax. Meaning, the wax on the black plate melts before the silver.

Question 27

What is the Leslie cube experiment? Summarise…

Answer 27

To prove that the amount of infrared radiation emitted from an object is not just dependant on its temperature, it’s also dependant on its material/surface. Summary: The Leslie cube is a hollow cube, half filled with boiling water, and has 4 different materials on each side, one Matt black, one shiny black, one Matt white and one silver. You would use a thermometer to measure the temp on each side of the cube and compare how it varies.

Question 28

What are the dangers of EM waves?

Answer 28

Em waves can be harmful to people as it enter living tissue. Radio waves - low frequency is don’t cause much damage. UV, x-rays, gamma rays - high frequency cause damage such as burns, skin cancer and ionising radiation (causing gene mutation etc.)

Question 29

How do you measure the risk of radiation Dose?

Answer 29

SIEVERTS, is a measure of the risk of harm from the body being exposed to radiation. The risk depends on the total amount radiation absorbed and how harmful it is. A sievert is pretty big so it’s often seen in doses of millisieverts (1000 msv = 1 sievert)