Waves

Question 1

What are waves?

Answer 1

A wave is a transfer of energy but not matter. It is caused by vibrations.

Question 2

What are the two types of waves?

Answer 2

• Transverse waves.

- Longitudinal waves.

Question 3

What is one use of a wave?

Answer 3

To transmit signals like WiFi and microwaves for telecommunication.

Question 4

What are some examples of waves?

Answer 4

Light waves, water waves, x-rays, sound waves.

Question 5

What are transverse waves?

Answer 5

Transverse waves are waves in which the motion of particles is at a right angles to the direction of motion of the wave. For eg. water waves, light waves.

Question 6

What are longitudinal waves?

Answer 6

Longitudinal waves are waves in which motion of particles is in the same direction as the direction of motion of the wave. Sound waves are the only type of longitudinal waves.

Question 7

What is the frequency of a wave?

Answer 7

The number of waves produced in 1 second by the source producing the wave. Unit: Hertz [Hz].

Question 8

What is the amplitude of a wave?

Answer 8

The height of the wave from the rest position. Unit: Metres [m].

Question 9

What is the wavelength?

Answer 9

The distance from a point to another point where the wave begins to repeat itself. Unit: Metres [m] and symbol λ.

Question 10

What is the wave speed?

Answer 10

A measure of how quickly the wave travels from its source. Unit: Metres per second [m/s].

Question 11

What is the period of a wave?

Answer 11

The time taken for one whole wave to pass a point. Unit: Seconds [s].

Question 12

Speed-frequency-wavelength formula

Answer 12

v = fλ

Question 13

Frequency-time formula

Answer 13

f = 1/T and T = 1/f

Question 14

How is the speed of sound different for different materials?

Answer 14

Sound energy travels through particles. In a solid, the particles are packed closely together so sound energy is passed easily through. In a liquid, the particles are further apart so sound energy takes longer to travel. In a gas, the they are further apart still and in a vacuum, there are no particles. Therefore sound energy does not travel in vacuum.

Question 15

What is refraction of light?

Answer 15

Refraction of light is the bending of light caused by a change in speed. It leads to a change in direction.

Question 16

Why does refraction occur?

Answer 16

If a wave travelling in one medium hits another medium, an an angle, then a part of the wave slows down while the rest stays at the original speed. This causes the wave to bend.

Question 17

How does light change when going from a rarer to a denser medium?

Answer 17

1) Slows down

2) Bends towards the normal [∠r < ∠i]

Question 18

How does light change when going from a denser to a rarer medium?

Answer 18

1) Speeds up

2) Bends away from the normal [∠r > ∠i]

Question 19

What is a convex lens?

Answer 19

A convex lens is a converging lens that brings light to a focus. A thicker/fat lens brings light to a focus in a shorter distance than a thinner lens.

Question 20

What is a concave lens?

Answer 20

A concave lens is a diverging lens that bends rays of light away from each other. It doesn’t have a real focus, but rather a virtual focus.

Question 21

What is the focus of a lens?

Answer 21

The focus of a lens is the point where parallel incident light rays meet (or appear to come from) after converging (or diverging).

Question 22

What is the focal length of a lens?

Answer 22

The focal length is the distance from the centre of the lens to the focal point/focus.

Question 23

What is diffraction?

Answer 23

Diffraction is the spreading out of waves when they go through a gap, or past the edge of a barrier.

Question 24

How does diffraction depend on the wavelength of a wave?

Answer 24

Greater the wavelength, greater the diffraction.

Question 25

What is an example of diffraction in real life?

Answer 25

Diffraction affects radio and television signals. Long wave radio signals are much less affected by buildings, hills, tunnels etc. than those of short wave or VHF radio, or television.

Question 26

What is a spectrum?

Answer 26

A spectrum is a range of values.

Question 27

What is the visible spectrum?

Answer 27

The visible spectrum is a range f colours that we can detect with our eyes.

Question 28

What is the electromagnetic [EM] spectrum?

Answer 28

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

Question 29

What are the different radiations in the EM spectrum?

Answer 29

In order of increasing wavelength and decreasing frequency:

• Gamma waves (10 ‐¹² to 10 ‐¹⁰ m)
• X-rays (10 ‐¹⁰ to 10 ‐⁸ m)
• Ultraviolet waves (10 ‐⁸ to 10 ‐⁷ m)
• Visible light (10 ‐⁷ to 10 ‐⁶ m) - Violet to Red
• Infrared waves (10 ‐⁶ to 10 ‐³ m)
• Microwaves (10 ‐³ to 10 ‐¹ m)
• Radio and TV waves (10 -¹ to 100 m)

Question 30

What are the sources, detectors and uses of gamma rays?

Answer 30

Sources - Radioactive nuclei
Detectors - Geiger counter, photographic film
Uses - To identify and treat cancer

Question 31

What are the sources, detectors and uses of X-rays?

Answer 31

Sources - When high speed electrons are slowed down very quickly
Detectors - Photographic film
Uses - To detect broken bones, medical diagnosis