Wave Characteristics (DP IB Physics: SL)

An unpolarised electromagnetic wave passes through 2 polarisers. The second polariser is at a clockwise angle a to the vertical.

When a = 225 ° what percentage of the unpolarised light is transmitted through both filters?

Cinema 3D glasses have polarising lenses aligned 90^o from each other. The left eye contains a horizontal polariser and the right lens contains a vertical polariser.

A person stands in front of a mirror and closes their left eye.

How do the glasses appear in the mirror?

The diagram shows a wave moving along a rope under tension in the direction shown.

Which of the following graphs, A to D, correctly shows the variation of displacement s with time t of the particle K in the rope?

Plane-polarised electromagnetic waves of radio frequency are transmitted by a vertical aerial and have an amplitude A. They are received by a second aerial rotated at angle compared to the transmitting aerial. 

Which of the following expressions is proportional to the power received by the second aerial?

A beam of plane-polarised light of intensity I is incident at right-angles to a polariser. The transmitted light has an intensity of . 

What is the angle, , between the plane of polarisation of the incident light and the polariser?

Use the values in the table to help.

A wave has frequency , intensity  and amplitude . The intensity of a wave is proportional to the square of the frequency.

A second similar wave has frequency and amplitude .

Which of the following is an expression for the intensity of the second wave, ?

Light from a lamp is incident on a polarising filter that has a horizontal transmission axis. The incident light has intensity  and the transmitted light has intensity . The filter is rotated by 2π.

Which graph correctly shows the variation of the ratio  with angle ?

Identify the pair of statements which are always true for electromagnetic waves

A.	Always travel at the same speed in a vacuum	Always obey the inverse square law
B.	Can undergo plane polarisation	Consist of electric and magnetic fields which have constant amplitude
C.	Have predictable reduction in intensity when passed through a polarising filter	Always travel at the same speed in a vacuum
D.	Consist of electric and magnetic fields which transfer energy	Are always polarised

The intensity of radiation from a star is given by . The intensity of light at the surface of one of its planets, a distance r from the star is . The distance between the star and a second planet is 3r. 

What is the intensity of light from the star on this second planet?

Light from the sun reflects off the surface of a pond. Some of the light continues into the water where it is refracted. 

Which line in the table gives the correct nature of the reflected and refracted light?

	Reflected	Refracted
A.	unpolarised	completely plane polarised
B.	completely plane polarised	completely plane polarised at right angles to the reflected light
C.	partially plane polarised	unpolarised
D.	partially plane polarised	partially plane polarised

Two polarisers have polarising axes that make an angle of 30° to each other. Unpolarised light of intensity is incident on the first polariser. Light of intensity passes between the first and second polarisers. After passing through the second polariser, light of intensity  emerges.

Considering the trigonometric ratios above, which line in the table correctly identifies the ratio and ?

A.
B.
C.
D.

A ripple tank is used to demonstrate the movement of progressive waves. In the tank, a wave is set in motion from left to right.

The wave is shown at time t = 0. Points X and Y on the wave have been marked.

Which option correctly shows the displacement-time graphs for both X and Y?

Two microwave transmitters are arranged to ensure that their waves undergo superposition and create a stationary wave made up of nodes and antinodes.

 

Which line correctly identifies the formula and a likely value for the minimum distance between the nodes of the stationary wave?

	formula	distance /cm
A.		30
B.		0.05
C.		30
D.		0.05

Two pulses are travelling towards each other.

What is a possible shape observed when the pulses undergo superposition?

Two wave fronts, each having amplitude A, travel towards each other, superpose, and continue with their motion.

What is the total amplitude during superposition and then the individual amplitudes following it?

	total amplitude during superposition	individual amplitudes following superposition
A.	A	A
B.	2A	< A
C.	2A	A
D.	4A	> A

Two waves which are in phase are produced by point sources at X and Y. The waves have amplitude A when they pass position Z.

In the arrangement shown, if the wavelength of the waves is 2 cm, what is the amplitude of the oscillation seen at Z?

A signal generator emits sound waves of amplitude A. The sound intensity at a distance d from the source is I.

What is the correct sound intensity detected at a distance   from the source when the source emits waves of amplitude 3A?

A beam of unpolarised light, I₀, is incident on a polarising filter X. The filter has been set up so that its transmission axis is parallel to that of a second filter Y.

Filter X is rotated by an angle which is approximately 30^o.

Which line correctly describes beam I₂ being emitted from filter Y?

	polarisation	intensity
A.	no change	different
B.	different	different
C.	no change	no change
D.	different	no change

Unpolarised light of intensity I₀ is incident on the first of two polarising sheets. Initially the transmission axes are parallel.

­­Which sheet must be rotated and by what angle so that light of intensity I₀ emerges from the second sheet?

You may use the fact that

cos 45 =

cos 60 = 

cos 90 = 0

	sheet	angle of rotation
A.	1 only	cos−1
B.	1 and 2	cos−1
C.	1 or 2	cos−1
D.	2 only	cos−1

The graph shows the displacement y, with distance x, of air molecules vibrating due to a sound wave of frequency 261 Hz travelling to the right.

Positive values of y indicate displacement of the particles to the right.

Which row correctly shows the positions of a compression (C) and rarefaction (R) at the moment shown and then 3.8 × 10⁻³ seconds later?

0.0 seconds

3.8 × 10−3 seconds

	C /cm	R /cm	C /cm	R /cm
A.	0.0	1.0	0.0	1.0
B.	1.0	2.0	2.0	3.0
C.	3.0	1.0	3.0	1.0
D.	3.0	1.0	4.0	2.0