Chapter 7. Waves

Question 1

What is wavelength?

Answer 1

The distance between two consecutive points on a wave.

Question 2

What is a wavefront?

Answer 2

A line joining points at the same position along a wave.

Question 3

Define period

Answer 3

The time taken for one complete oscillation.

Question 4

What is frequency?

Answer 4

The number of oscillations per unit time
frequency,f = 1/period, T

Question 5

State the wave equation

Answer 5

speed,c = frequency,f x wavelength,

Question 6

What is dispersion?

Answer 6

This is when different wavelengths travel at different speeds when a wave travels through a medium, the waves separate out

Question 7

What is amplitude?

Answer 7

The maximum displacement of a particle from rest position

Question 8

Note

Answer 8

energy is directly proportional to amplitude squared

Question 9

What is intensity?

Answer 9

The energy per second per square metre(Wm^-2)
I = P(power of source, P)/4 pi r²

Question 10

Note

Answer 10

The distance of the source of a wave is directly proportional to the radius of its circle of influence

Question 11

Define anti-phase

Answer 11

When waves have exactly opposite phases, phase difference of 180 degrees

Question 12

Note

Answer 12

Waves with a phase difference of 2pi 4pi radians and so on are in phase so 3pi radians phase difference is actually pi radians phase difference
One full cycle is 360 degrees

Question 13

What is a transverse wave?

Answer 13

A progressive wave in which the displacement is perpendicular to the velocity of the wave.

Question 14

What is a longitudinal wave?

Answer 14

A progressive wave in which the displacement is in the same direction as the velocity of the wave.

Question 15

Note

Answer 15

I(intensity) is directly proportional to amplitude squared

Question 16

Note

Answer 16

Gamma radiation is emitted by radioactive nuclei, X-rays are produced when high-speed electrons decelerate quickly. High energy X-rays have shorter wavelengths than low-energy gamma rays. Visible light ranges from 400nm(violet light) to 700nm(red light)

Question 17

Note

Answer 17

Speed of electromagnetic waves through a vacuum is 3.00 x 10⁸ms^-1

Question 18

Note

Answer 18

electromagnetic waves are made of an electric and magnetic field both in phase and 90 degrees to each other and to the direcction of travel

Question 19

What does it mean when a wave is plane polarised?

Answer 19

The vibrations of the wave are only shown in one plane.

Question 20

What is a progressive wave?

Answer 20

A wave that transfers energy from one point to the other without transfering matter

Question 21

Formula for phase difference

Answer 21

distance between two particles / wavelength x 360 degrees

Question 22

Note

Answer 22

Intensity is directly proportional to amplitude squared

Question 23

Note

Answer 23

Make sure you understand the time base settings stuff

Question 24

What is the doppler effect?

Answer 24

The frequency change due to the relative motion between a source of sound and an observer

Question 25

Note

Answer 25

f₀ = f_sv/(v-v_s) for a source approaching the observer where
f₀ is the observed frequency
f_s is the frequency of the source
v is the speed of the wave
and v_s is the speed of the source
the negative sign changes to a positive for a source moving away from the observer.

Question 26

Properties of electromagnetic waves

Answer 26

1. They are propagated by varying electric and magnetic fields at right angles to each other.
2. They can travel through a vacuum.
3. They travel with a constant speed of 2.998 x 10⁸ m s^-1 in a vacuum. The speed and wavelength change in different media but the frequency remains constant. The wave equation, c = f λ can be applied to find f or λ, if the speed is known.
4. They travel in straight lines and obey the inverse square law for intensity.
5. They are unaffected by electric and magnetic fields.
6. They exhibit the wave properties of: reflection, refraction, diffraction and interference.
7. They can be plane polarised because they are transverse.

Question 27

Orders of magnitude of electromagnetic waves(wavelength in m)

Answer 27

radio waves - >10⁶ to 10^-1
microwaves - 10^-1 to 10^-3
infrared - 10^-3 to 7 x 10^-7
visible light - 7 x 10^-7(red) to 4 x 10^-7(violet)
ultraviolet - 4 x 10^-7 to 10^-8
X-rays - 10^-8 to 10^-13
gamma rays - 10^-10 to 10^-16

Question 28

Wave, Origin, Detection, Uses

Answer 28

Radio - oscillating current in aerials - tuned circuit - communication
Micro - directly produced in wave guides - diodes and wave guide tubes - radar, microwave cooking
infrared - hot bodies, molecular vibrations - thermopile - heating photography
visible light - very hot bodies, filament lamps, electron transitions in outer orbit - eye photography - photo-synthesis
ultraviolet - extremely hot objects, sparks, electron transitions - fluorescence photocell - causes suntan, kills germs
X rays - bombarding metal targets with electrons - Geiger tube, photoelectric effect, photography - causes ionization, fluorescence, X ray photography

γ rays - radioactive decay - Geiger tube - medicine, cancer treatment, tracers

Question 29

State Malus’s law

Answer 29

The intensity of the transmitted light varies as the square of the cosine of the angle between the two planes of transmission.
I_{T = I0cos^{2θ
where
I0 is the intensity of the incident and IT is the transmitted intensity at an angle θ}}