Chapter 7: Waves

Question 1

What are progressive waves?

Answer 1

Progressive waves transfer energy without transferring matter; they move through a medium or vacuum of space.

Question 1

What instrument can be used to demonstrate wave effects?

Answer 1

Ripple tank

Question 1

What is displacement (waves)?

Answer 1

Distance from its equilibrium position.
It is a vector quantity; it can be positive or negative. Measured in metres.

Question 1

What is amplitude (waves)?

Answer 1

Maximum displacement of a particle in the wave from its equilibrium position. Measured in metres.

Question 1

What are transverse waves?
And give some examples

Answer 1

A wave in which the particles oscillate perpendicular to the direction of motion and energy transfer.
Examples: EM waves (radio, visible light, UV) and vibrations on a guitar string

Question 1

What are longitudinal waves? With examples

Answer 1

A wave in which the particles oscillate parallel to the direction of motion and energy transfer.
Examples: sound waves

Question 2

What is wavelength (waves)?

Answer 2

The distance between two points on successive oscillations of a wave that are in phase. Measured in metres.

Question 2

What are standing waves.

Answer 2

No net energy transfer and oscillate with fixed nodes and antinodes.

Question 3

What direction is the wave travel in vibration of a rope?

Answer 3

Perpendicular to the vibration of rope.

Question 4

What direction is the wave travel in vibration in spring?

Answer 4

Parallel to the vibration of coils.

Question 5

What is frequency (of a wave) and its formula?

Answer 5

Number of complete oscillations per unit time. Measured in Hertz

f = 1/T

Question 6

What is period (of waves)?

Answer 6

Time period is the time taken for one complete oscillation or cycle of the wave (measured in seconds).

Question 7

What is phase difference of a wave?

Answer 7

The phase difference tells us how much a point or a wave is in front or behind another.

When the crests or troughs are aligned, the waves are in phase. (360 - 2pi)
When the crest of one wave aligns with the trough of another, they are in anti phase. (180 - pi)

Question 8

What is a cathode ray oscilloscope and how does it work (AC, DC)?

Answer 8

A cathode ray oscilloscope is a laboratory instrument used to display, measure and analyse waveforms of electrical circuits.

An A.C. current on an oscilloscope is represented as a transverse wave.

An D.C. current on an oscilloscope is represented as a horizontal line at the relevant voltage.

Question 9

What is on the x and y axis of a cathode ray oscilloscope diagram?

Answer 9

x - axis : time
y - axis : voltage (or y gain)

Question 10

What is time base?

Answer 10

How many seconds each division represents.

Question 11

What is the wave equation and how is or derived?

Answer 11

v = f λ

v = d/t = 1/t * d = f * λ

Question 12

Relationship between wavelength and frequency using formula

Answer 12

As wavelength increases, the frequency decreases.
As wavelength decreases, the frequency increases.

Therefore wavelength and frequency are inversely proportional to each other.

Question 13

c (speed of light) of electromagnetic waves

Answer 13

3 * 10^8

Question 14

Intensity definition with formula.

Answer 14

Amount of energy passing through a unit area per unit time is the intensity of a wave.

I = P/A

I = W/m^2

Question 15

Which two factors is intensity also proportional to?

Answer 15

Amplitude squared.
Frequency squared.

Question 16

What is the inverse square law?

Answer 16

Intensity it proportional to 1/r^2

Question 17

What is a spherical wave and explain?

Answer 17

A spherical wave is a wave from a point source which spreads out equally in all directions. The area the wave passes through is the surface area of the sphere: 4pi r^2

Question 18

What are mechanical waves?

Answer 18

A type of progressive wave that also transfers energy but requires a medium to propagate.

Question 19

What type of waves are EM waves?

Answer 19

Electromagnetic waves are progressive waves NOT mechanical waves hence don’t require medium to travel through.

Question 20

What are the two main types of mechanical waves?

Answer 20

Transverse and Longitudinal

Question 21

All longitudinal waves cannot…?

Answer 21

Cannot be polarised Cannot travel though vacuum (require medium)

Question 22

What is rarefraction and compression in longitudinal waves?

Answer 22

A rare fraction is an area of low pressure, with the particles being further apart. A compression is a an area of high pressure, with the particles being closer to each other.

Question 23

“Direction of propagation” meaning

Answer 23

Energy transfer

Question 24

Doppler shift formula

Answer 24

f(o) = f(s)(v/(v +- v(s)) If the source is moving towards, minus. If the source is moving away, add.

Question 25

Electromagnetic Waves properties

Answer 25

They are all: Transverse waves Travel in vacuum Same speed in vacuum (3*10^8 m/s)

Question 26

EM spectrum names

Answer 26

Radio waves Microwaves Infrared Visible light Ultra violet X rays Gamma rays

Question 27

EM waves approximate wavelengths

Answer 27

In metres: Radio waves: > 0.1 Microwaves: 0.1 — 1*10^-3 Infrared: 1*10^-3 — 7*10^-7 Visible light: 7*10^-7 — 4*10^-7 Ultraviolet light: 4^*10^-7 — 1*10^-8 X rays: 1*10^-8 — 4*10^-13 Gamma rays: 4*10^-13 — 10^-16

Question 28

Wavelength of visible light

Answer 28

400nm to 700nm

Question 29

How are electromagnetic waves generated?

Answer 29

Combination of electric and magnetic fields. They are a type of transverse wave that oscillates in more than one plane. An electric field oscillates on one plane, and a magnetic field on a different plane. Both planes are at right angles to each other and to the direction of wave motion.

Question 30

What does polarisation do?

Answer 30

Restricts vibrations to one plane of oscillation. An unpolarised wave oscillates in many planes of oscillation. A vertically polarised wave oscillates only in the vertical plane. A horizontally polarised wave oscillates only in the horizontal plane.

Question 31

State an example of polarisation.

Answer 31

Polaroid sunglasses. Contain vertically oriented polarising filters.

Question 32

Malus’s Law

Answer 32

I = 1(0)/2 I = I(0) cos^2 θ

Question 33

Phase difference formula

Answer 33

Ф = ∆x/λ