Name:_________________________________________ Period:______
Date:______________
IB-2 Diffraction Practice
1.
This question is about diffraction and resolution.
(a)
Light from a monochromatic point source S1 is incident on a narrow rectangular slit.
After passing through the slit, the light is incident on a screen some distance away from the
slit. The graph shows how the intensity distribution on the screen varies with the angle θ
shown in the diagram.
(i)
The width of the slit is 4.0 × 10–4 m. Use data from the graph to calculate the
wavelength of the light.
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(2)
[Type text]
(ii)
An identical source S2 is placed close to S1 as shown.
The images of the two sources on the screen are just resolved according to the
Rayleigh criterion. On the graph above, draw the intensity distribution of the second
source.
(1)
(b)
The Very Large Array (VLA) is used to analyse radio signals from distant galaxies.
The combined diameter of the VLA is 36 km. A region of linear size L inside the radio
galaxy M87 emits radio waves with a frequency of 43 GHz. The galaxy is a distance
4.7 × 1023 m from Earth. The VLA can just resolve the radio emitting region.
Estimate the value of L.
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(3)
(Total 6 marks)
IB Questionbank Physics
2
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2.
This question is about diffraction and resolution.
(a)
A parallel beam of monochromatic light is incident on a narrow rectangular slit. After
passing through the slit, the light is incident on a distant screen.
Point X is the midpoint of the slit.
(i)
On the axes below, sketch a graph to show how the intensity of the light on the
screen varies with the angle θ shown in the diagram.
(3)
(ii)
The wavelength of the light is 520 nm, the width of the slit is 0.04 mm and the screen
is 1.2 m from the slit. Show that the width of the central maximum of intensity on the
screen is about 3 cm.
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(2)
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[Type text]
(b)
Points P and Q are on the circumference of a planet as shown.
By considering the two points, outline why diffraction limits the ability of an astronomical
telescope to resolve the image of the planet as a disc.
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(3)
(Total 8 marks)
IB Questionbank Physics
4
[Type text]
3.
In two separate experiments monochromatic light is incident on a single slit. The diagrams show
the diffraction patterns obtained on a screen far from the slit. In the top diagram the wavelength of
light is λ1 and the slit width is b1. In the bottom diagram the wavelength of light is λ2 and the slit
width is b2.
In each experiment the distance between the slit and the screen is the same. Which of the
following may be deduced?
A.
B.
1
b1
1
b1


2
b2
2
b2
C.
b1 < b2
D.
λ1 > λ2
(Total 1 mark)
4.
This question is about the diffraction of light.
(a)
(i)
Describe what is meant by the diffraction of light.
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(2)
IB Questionbank Physics
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[Type text]
(ii)
A parallel beam of monochromatic light from a laser is incident on a narrow slit.
The diffracted light emerging from the slit is incident on a screen.
(not to scale)
The centre of the diffraction pattern produced on the screen is at C. On the axes
sketch a graph to show how the intensity I of the light on the screen varies with the
distance d from C.
(3)
(iii)
The slit width is 0.40 mm and it is 1.9 m from the screen. The wavelength of the light
is 620 nm. Determine the width of the central maximum on the screen.
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(3)
IB Questionbank Physics
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[Type text]
(b)
(i)
When two separate lasers are used as sources, the images of the slit formed by the
light from each laser are resolved. State what is meant by the term resolved in this
context.
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(1)
(ii)
A car, with its two headlights switched on, is approaching an observer who has good
eyesight. Outline why, at a long distance from the observer, the images of the
headlights of the car are not resolved by the observer.
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(4)
(Total 13 marks)
5.
This question is about microwaves.
(a)
Radiation from a microwave transmitter passes through a single narrow slit. A receiver is
placed several metres beyond the slit. The receiver can be moved between point A and
point B along a line parallel to the slit.
(i)
On the axes below, sketch a graph to show the variation of intensity of the
microwave radiation with distance along line AB. The graph has been started for
you.
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[Type text]
(3)
(ii)
The width of the narrow slit is reduced. State and explain two effects on the intensity
distribution you have shown in (a)(i).
Effect: ...............................................................................................................
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Explanation: ......................................................................................................
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Effect: ...............................................................................................................
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Explanation: ......................................................................................................
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(4)
(b) Standing waves are formed in microwave ovens. Suggest why it is desirable that food is
rotated while being cooked in the microwave.
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(3)
(Total 10 marks)
IB Questionbank Physics
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