Wave motion

Question 1

What are mechanical waves

Answer 1

Mechanical waves are waves produced in a deformable or elastic medium. The wave motion is transmitted by the particles of the medium oscillating to and fro

Question 2

What are electromagnetic waves

Answer 2

• Consist of electric and magnetic fields that oscillate at right angles to each other and to the direction of energy transfer
• Transverse waves
• Can travel through vacuum
• Travel with the same speed
• Show all properties common to wave motions

Question 3

What are progressive waves

Answer 3

Progressive waves transfer energy from one place to another without the transfer of matter

Question 4

What are transverse waves

Answer 4

Transverse waves are waves in which the displacement of the particles of the medium is perpendicular to the direction of energy transfer

Question 5

What are longitudinal waves

Answer 5

Longitudinal waves are waves in which the displacement of the particles of the medium is parallel to the direction of energy transfer

Question 6

What is frequency

Answer 6

f = 1/T

Question 7

What is wave speed

Answer 7

v = λ/T
v = fλ

Question 8

Phase difference in displacement-distance graphs

Answer 8

Φ/2π = x/λ

Question 9

Phase difference in displacement time graphs

Answer 9

Φ/2π = t/T

Question 10

What is intensity

Answer 10

Intensity of a wave is defined as the rate of energy flow per unit cross sectional area perpendicular to the direction of energy transfer

I = E/tS = P/S

Question 11

The energy transported by a progressive wave is proportional to _______

Answer 11

the square of its amplitude

E α A^2

Question 12

The intensity of a wave is proportional to _______

Answer 12

the square of its amplitude

I α A^2

Question 13

Intensity of a wave at distance r

Answer 13

I = P/4πr^2

I α 1/r^2

Question 14

Amplitude A is inversely proportional to _________

Answer 14

the distance r form the point source

A α 1/r

Question 15

What is a plane polarised wave

Answer 15

A wave is plane polarised if the oscillations are in one direction perpendicular to transfer of energy

Question 16

What is plane-polarised light

Answer 16

The electric field at every point oscillates in the same fixed point known as the plane of polarisation

Question 17

What is Malus’ Law

Answer 17

I=I₀cos²θ

Question 18

What is the principle of superposition

Answer 18

When 2 or more waves of the same kind exist simultaneously at a point in space, the resultant displacement of the waves at any point is the vector sum of the displacement due to each wave acting independently

Question 19

What are stationary waves

Answer 19

When 2 progressive waves of equal amplitude and equal frequency travelling with the same speed in opposite directions are superposed, a stationary wave is formed

Question 20

Properties of stationary waves

Answer 20

1. The wave does not move along and the particles vibrate with the same frequency
2. Particles at nodes do not oscillate at all
3. Midway between nodes particles vibrate with the largest amplitude, known as anti-nodes
4. Distance btw nodes = distance btw anti-nodes = λ/2
5. All particles btw adjacent nodes are in phase. Particles btw a pair of nodes are anti-phase with the adjacent pair
6. There is no net transfer of energy from one end to the other. At all points except the nodes, energy is continuously changing btw KE and PE

Question 21

Stationary waves in stretched strings

Answer 21

General equation: L = (n x λn)/2

Resonant frequency: fn = nv/2L = nf

Question 22

Stationary waves in closed pipes

Answer 22

f1 = v/4L

Resonant frequencies are odd-integral multiples of the fundamental frequency f1

Question 23

Stationary waves in open pipes

Answer 23

f1 = v/2L

Resonant frequencies are integral multiples of the fundamental frequency f1