Waves

Question 1

Are electro-magnetic waves transverse or longitudinal?

Answer 1

Transverse

Question 2

True or false:

Angle of incidence=angle of refraction

Answer 2

False

The angle of incidence=the angle of reflection

Question 3

When a wave passes from a low density medium to a high density medium the Ray bends __________ the normal.

Answer 3

Towards

Question 4

When a wave passes into a medium of a greater density, what happens to the speed of the wave?

Answer 4

The speed is slower

Question 5

When a wave passes into a medium of a greater density, what happens to the wavelength of the wave?

Answer 5

It becomes shorter.

Question 6

How do you calculate the refractive index?

Answer 6

Sin i/ sin r

Question 7

Define refractive incidence.

Answer 7

The ratio of wave velocities in the two media. The refractive index “n” relates to the boundary between two media.

Question 8

When does maximum diffraction occur?

Answer 8

When the gap size is similar to the wavelength of the wave

Question 9

Are ANTINODES constructive or destructive?

Answer 9

Constructive

Question 10

Are NODES constructive or destructive?

Answer 10

Destructive

Question 11

What is the principle of superposition of waves?

Answer 11

When two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point.

Question 12

What is rectilinear propagation?

Answer 12

Waves travel in straight lines.

Question 13

Why is a laser used during the demonstration of two slit wave interference experiments?

Answer 13

The light is monochromatic (light of only one colour).

Question 14

What is POLARISATION?

Answer 14

When all oscillations on one plane of a wave are removed.

Question 15

True or false:

Polarisation can only occur in both transverse and longitudinal waves.

Answer 15

False: polarisation can only occur in transverse waves.

Question 16

What are the the two axes on a CRO and what does CRO stand for?

Answer 16

CRO = Cathode Ray Oscilloscope

Y axis: voltage
X axis: time

Question 17

What is the INTENSITY of a wave?

Answer 17

The energy falling on unit cross-sectional area per second ➡️ Intensity=power/area

Question 18

True or false:

Intensity is directly proportional to amplitude

Answer 18

False:

I is directly proportional to amplitude squared

Question 19

Distinguish between longitudinal and transverse waves.

Answer 19

Transverse waves have oscillations perpendicular to the direction of propagation (energy transfer), whereas the oscillations of longitudinal waves are parallel to the propagation.

Question 20

True or false:

Polarisation can occur in both transverse and longitudinal waves.

Answer 20

FALSE

polarisation can only occur in transverse waves because the oscillations are perpendicular to the direction of wave propogation so there are many different orientations, which can be polarised.

Question 21

Define a stationary wave

Answer 21

A stationary wave is a wave produced by the superstition of a wave and its reflection.

Question 22

What is meant by ‘progressive wave’?

Answer 22

A wave that transfers energy and momentum away from the source.

Question 23

Distinguish between progressive waves and stationary waves by making reference to energy transfer.

Answer 23

Progressive waves, unlike stationary waves, transfer energy.

Question 24

Why can most graphical representations of a sound wave in a closed pipe be misleading?

Answer 24

Sound waves are longitudinal rather than transervse and so are not, as depicted, smooth curves. The diagrams represent the oscillations of the particles.

Question 25

Stationary waves can be produced in closed pipes Why can standing waves also be produced in open ended pipes?

Answer 25

The change in air pressure at the end of the pipe means the wave can be reflected and thus standing waves can be formed by the superposition of the wave and its reflection.

Question 26

Stringed instruments use standing waves. | How is the frequency altered?

Answer 26

Changing the frequency can help change the note. The frequency depends on: 1) the mass per unit volume of the string 2) The tension of the string (can be adjusted when tuning the instrument) 3) the length of the string (increased or decreased by the musicians fingers)

Question 27

A student stands midway between a pair of speakers, which are oscillating at 400Hz and 401Hz respectively. The sound waves produced by these speakers have equal amplitudes. Describe and explain what she hears.

Answer 27

The student will hear a periodic variation in the loudness of the sound (beats) The phase difference between the two waves continually, and periodically changes due to the slight difference in frequency. When the waves are in phase they will reinforce each of her, increasing the loudness of the sound. As the two waves move out of phase they cancel each other out and the loudness of sound decreases. The frequency of the beating effect will be 1Hz.

Question 28

Distinguish between a progressive wave and stationary wave by making reference to amplitude of vibration of neighbouring particles.

Answer 28

In a stationary wave the amplitude varies with position along waves ( from a maximum at ANTINODES and 0 at nodes). In progressive waves - all particles have the same amplitude (at each point the displacement varies over a cycle).

Question 29

Distinguish between a progressive wave and stationary wave by making reference to phase angle between particles.

Answer 29

Over one wavelength of a progressive wave, each particle has a different phase angle. In a stationary wave, all the particles in one segment have the same phase angle, which is opposite to all the particles in the adjacent segment.

Question 30

Show how the principle of superposition of light waves can be used to explain the formation of interference fringes when youngs double-slit is used. (8 marks)

Answer 30

Alternating bright fringes and dark fringes: Bright - regions of maxima formed by the waves from each source (slit) arriving in phase, causing constructive interference. This occurs when the path difference of the waves from each slit is a whole number of wavelengths. Dark - regions of minima, formed by the waves from each slit arriving in anti-phase, causing destructive interference. This occurs when the path difference is an odd number of half wavelengths.

Question 31

State what is meant by threshold frequency.

Answer 31

The minimum frequency required to free electrons (due to photons of adequate size being emitted).

Question 32

Describe what is meant by a plane polarised wave

Answer 32

A wave that has had all but one plane, perpendicular to the plane, removed by polarisation.

Question 33

Explain the meaning of the term phase difference

Answer 33

Relates to the oscillation of two points on the wave. How far out of step one oscillation is from the other.

Question 34

Explain how an under what conditions a stationary soundwave is formed in an open ended tube.

Answer 34

The wave reflected at the end of the pipe interferes with the incident wave to produce a resultant wave with nodes and ANTINODES. both ends must be anti-nodes.

Question 35

State the principle of superposition of waves

Answer 35

When two waves overlap the resultant displacement is the vector sum of the individual displacements

Question 36

Explain the term coherent

Answer 36

Waves with a constant phase difference