Waves

Question 1

How do waves travel ?

Answer 1

Waves travel through a medium (substance). The particles oscillate (vibrate) and transfer energy. The particles stay in the same place.

Question 2

Wavelength

Answer 2

the distance between adjacent waves (ie. from peak to peak or trough to trough)

Question 3

Amplitude

Answer 3

the maximum displacement from a waves undisturbed position (the horizontal mid-line)

Question 4

Frequency

Answer 4

the number of complete waves that pass a point every second. 1 wave per second has a frequency of 1Hz (hertz).

Question 5

Time period

Answer 5

the time for a complete cycle of a wave

Question 6

Time period equation….

Answer 6

𝑇= 1/𝑓

Question 7

In transverse waves…

Answer 7

The oscillations (vibrations causing the wave) are perpendicular (90°) to the direction of energy transfer.

Question 8

Examples of transverse waves

Answer 8

• all EM waves
• waves on water
• a wave on a string

Question 9

In longitudinal waves…..

Answer 9

The oscillations are parallel to the direction of energy transfer.

Question 10

Wave speed equation

Answer 10

𝑉=𝑓𝜆

Question 11

Example of longitudinal wave..

Answer 11

Sound waves travel as a longitudinal wave in air.

Question 12

Refraction

Answer 12

When waves change speed when they cross a boundary between two materials of different density.

Question 13

If the wave enters a medium of higher density at an angle…..

Answer 13

the ray bends towards the normal

Question 14

If it enters a medium along the normal then….

Answer 14

the wave does not change direction but the wavelength and speed decrease. )

Question 15

Why does refraction happen ?

Answer 15

The part of the wave front that enters the more dense medium first, slows down as the rest of the wave front continues at the same speed but has to travel further. The difference in distance and speed causes the wave to refract

Question 16

Wave experiment required

practical…

Answer 16

To measure the speed of sound:

1) two microphones held by a speaker (plugged into to a signal generator) can be connected to an oscilloscope.
2) One microphone is moved away from the speaker until the waves line up on the oscilloscope. The distance between the microphones is the wavelength. 3)Use V = fλ to find the speed of sound (f = whatever frequency the signal generator is set to). The speed of sound in air is 330 m/s.
4) The speed of water ripples and waves on a string can be investigated and calculated using the waves speed equation.

Question 17

The electromagnetic spectrum

Answer 17

radio waves = 1-10(4)m = λ
micro waves = 10(-2)m = λ
infrared waves = 10(-5)m = λ
visible light  = 10(-7)m = λ
ultra violet  = 10(-8)m = λ
x-rays  = 10(-10)m = λ
gamma rays  = 10(-15)m = λ

wavelength decreases as you go up
frequency increases as you go up

Question 18

Do all electromagnetic waves travel at the same speed through a vacuum ?

Answer 18

all electromagnetic waves travel at the same speed through a vacuum

Question 19

Ultrasound

Answer 19

Ultrasound waves have a frequency higher than the upper limit for human hearing - above 20,000 Hertz (Hz).

Question 20

Uses of ultrasound include:

Answer 20

• breaking kidney stones

- cleaning jewellery

Question 21

P-waves

Answer 21

• longitudinal
• faster than S-waves
• can travel through solids and liquids

Question 22

S-waves

Answer 22

• transverse
• slower than P-waves
• can travel through only solids

Question 23

Seismic Waves

Answer 23

Shock waves travelling through the Earth, usually caused by an earthquake

Question 24

What is a lens ?

Answer 24

A lens is a shaped piece of transparent glass or plastic that refracts light.

Question 25

Why is light refracted ?

Answer 25

When light is refracted it changes direction due to the change in density as it moves from air into glass or plastic.

Question 26

Uses of lens

Answer 26

• cameras, telescopes, binoculars, microscopes and corrective glasses.