IB Physics SL C.3 Wave Phenomena

[Maximum number: 3]

A group of students is investigating refraction in a semi-circular glass block.

Light from a ray box enters the curved side of the block. The light passes through the block and leaves, refracted, at P .

(a)

Outline how the students can ensure that the light is not deflected at the curved surface.

[ 1 ]

measure P to be at the centre of the flat edge/side so that incident rays are aimed at P /go through radial lines

OR

check that the incident angle is $0^{\circ}$ at every point of incidence

[1]

(b)

They plot a graph of the variation with the sine of $\theta_{i}$ of the sine of $\theta_{r}$ .
They add uncertainty bars for $\sin \theta_{r}$ for the first and last data point and draw the best-fit line.

[ 2 ]

(i)

Determine the value of the refractive index of the glass with its absolute uncertainty.

[ 2 ]

States gradient gives the value of the refractive index

OR

n=1.5 $n=1.5 \pm 0.2$

MP1 can be shown as an equation.

Candidates may calculate the uncertainty by using the gradient of the line found in cii) or finding the average of the max and min lines of best fit.

Look for working leading to $0.1 \leq \Delta n \leq 0.2$ .

[Maximum number: 8]

Monochromatic light enters the base of a plastic beaker that contains water with an oil layer floating on it. A student draws a diagram to show the directions the light takes as it passes through the layers. The student's diagram has one error at position A and one error at position B. The refractive indices of the materials are shown on the diagram.

The light is refracted at an angle of $32^{\circ}$ when it enters the plastic layer as shown.

(a)

Identify, with a reason, the error in the student's diagram for

[ 4 ]

(i)

light crossing the plastic-water interface (position A).

[ 2 ]

the angle of refraction ought to be greater than the angle of incidence OR the ray should refract away from the normal
because ray goes from high refractive index/<<optically>> more dense/slower medium to
low refractive index/optically less dense/faster medium

Marking guidance:

Do not allow use of e.g $n_{1}$
unless medium one is
described e.g. $n_{\text {air }}$

(ii)

light at the water-oil interface (position B).

[ 2 ]

(b)

Calculate the angle of incidence at the air-plastic interface.

[ 2 ]

$\begin{aligned} \text { Use of Snell's Law }<\frac{\sin i}{\sin r}=\frac{1.60}{1} \gg i=\sin ^{-1}<1.60 \times \sin 32^{\circ}>=58<^{\circ} \gg \end{aligned}$

'Use of' requires a substitution NOT just a statement of a formula

Accept 1.0 rad (unit must be included to show a deliberate attempt to use rad rather than a calculator mistake)

(c)

Calculate the critical angle for the plastic-water interface.

[ 2 ]

$\begin{aligned} \frac{\sin i}{\sin r}=\frac{1.33}{1.60} \text { and } \sin r=1 i=\lessdot \sin ^{-1} 0.831 »=56<^{\circ} \gg \end{aligned}$

Accept 0.98 rad (unit required)

[Maximum number: 3]

This question is in two parts. Part 1 is about a thermistor circuit. Part 2 is about vibrations and waves.
Part 1 Thermistor circuit
The circuit shows a negative temperature coefficient (NTC) thermistor X and a $100 \mathrm{k} \Omega$ fixed resistor R connected across a battery.

The battery has an electromotive force (emf) of 12.0 V and negligible internal resistance.

Part 2 Vibrations and waves

The cone and dust cap D of a loudspeaker L vibrates with a frequency of 1.25 kHz with simple harmonic motion (SHM).

A second loudspeaker S emits the same frequency as L but vibrates out of phase with L . The graph below shows the variation with time t of the displacement x of the waves emitted by S and L .

On the graph, sketch the variation with t of x for the wave formed by the superposition of the two waves. be marked.

Agreement at all zero displacements.
Maxima and minimum at correct times.
Constant amplitude of $1.60\ \text{mm}$ .

Figure for Answer to Question 3 — IB Physics SL

[Maximum number: 1]

A group of students is investigating refraction in a semi-circular glass block.

Light from a ray box enters the curved side of the block. The light passes through the block and leaves, refracted, at P .

Outline how the students can ensure that the light is not deflected at the curved surface.

measure P to be at the centre of the flat edge/side so that incident rays are aimed at P /go through radial lines

OR

check that the incident angle is $0^{\circ}$ at every point of incidence

[1]

[Maximum number: 2]

A group of students is investigating refraction in a semi-circular glass block.

Light from a ray box enters the curved side of the block. The light passes through the block and leaves, refracted, at P .

They plot a graph of the variation with the sine of $\theta_{i}$ of the sine of $\theta_{r}$ .
They add uncertainty bars for $\sin \theta_{r}$ for the first and last data point and draw the best-fit line.

Determine the value of the refractive index of the glass with its absolute uncertainty.

States gradient gives the value of the refractive index

OR

n=1.5 $n=1.5 \pm 0.2$

MP1 can be shown as an equation.

Candidates may calculate the uncertainty by using the gradient of the line found in cii) or finding the average of the max and min lines of best fit.

Look for working leading to $0.1 \leq \Delta n \leq 0.2$ .

[Maximum number: 2]

Monochromatic light enters the base of a plastic beaker that contains water with an oil layer floating on it. A student draws a diagram to show the directions the light takes as it passes through the layers. The student's diagram has one error at position A and one error at position B. The refractive indices of the materials are shown on the diagram.

The light is refracted at an angle of $32^{\circ}$ when it enters the plastic layer as shown.

Calculate the critical angle for the plastic-water interface.

$\begin{aligned} \frac{\sin i}{\sin r}=\frac{1.33}{1.60} \text { and } \sin r=1 i=\lessdot \sin ^{-1} 0.831 »=56<^{\circ} \gg \end{aligned}$

Accept 0.98 rad (unit required)

[Maximum number: 1]

This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

The light from the laser is coherent and monochromatic. Outline what is meant by the term

coherent.

[Maximum number: 1]

This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

The distance from the two slits to the screen is 1.5 m . The distance BC is 1.8 mm and the distance between the slits is 0.30 mm .

State the path difference, in metres, between the waves that meet at B .

[Maximum number: 1]

This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

State the phase difference between the light waves from the two slits that meet at B .

$180^{\circ} / \pi \mathrm{rad}$ ;

Marking guidance:

Do not accept $\frac{\lambda}{2}$ .

[Maximum number: 3]

This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

The distance from the two slits to the screen is 1.5 m . The distance BC is 1.8 mm and the distance between the slits is 0.30 mm .

Show that the laser produces light of wavelength equal to 720 nm .

use of $\lambda=\frac{s d}{D}$ ;
$s=\underline{2} \times 1.8(\mathrm{~mm})$ ;
(award this mark for any evidence for the factor of 2 )
$\lambda=\frac{2 \times 1.8 \times 10^{-3} \times 0.30 \times 10^{-3}}{1.5} /$ OWTTE;
( $=7.2 \times 10^{-7} \mathrm{~m}$ )

Exact answer is given, award marks for correct working.

[Maximum number: 2]

This question is about diffraction and resolution.

Monochromatic light is incident normally on a single narrow slit and gives rise to a diffraction pattern on a screen.

Two lamps emit light of wavelength 620 nm . The lights are observed through a circular aperture of diameter 1.5 mm from a distance of 850 m . Calculate the minimum distance between the lamps so that they are resolved.

equating $1.22 \frac{\lambda}{b}$ to $\frac{x}{D}$ ;
0.43 (m);

IB Physics SL C 3 Wave Phenomena Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (i)

Question 2

Question (a)

Question (i)

Question (ii)

Question (b)

Question (c)

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11