6.5 Required practical: reflection and refraction of light
9 exam questions worth 25 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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When a ray of light enters a glass block at an angle, it bends:
Choose one answer.
Correct Not quite: the answer is Towards the normal
Mark scheme
B: Towards the normal
Model answer
Towards the normal (B).
State why the normal is drawn when measuring the angles of incidence and refraction.
Mark scheme
all angles are measured from the normal
Model answer
All angles are measured from the normal.
The student measures an angle of incidence of 40° and an angle of refraction of 26°. State what these measurements show about the speed of light in the glass compared with in air.
Mark scheme
the ray bends towards the normal (1); so light travels more slowly in glass (1)
Model answer
The ray bends towards the normal, which shows that light travels more slowly in glass than in air.
Describe how the emergent ray compares with the incident ray when light passes through a rectangular glass block. Explain your answer.
Mark scheme
the emergent ray is parallel to the incident ray (1); but shifted to the side (1); because the two surfaces are parallel, so the bending away on exit cancels the bending towards on entry (1)
Model answer
The emergent ray is parallel to the incident ray but moved sideways. The surfaces are parallel, so the amount it bends away from the normal when leaving cancels the bending towards the normal on entering.
Describe the steps to draw the path of the ray inside a glass block, without being able to see it directly.
Mark scheme
mark where the ray enters and where it leaves the block (1); mark points along the incident and emergent rays (1); remove the block and join the incident ray to the emergent ray (1); join the entry and exit points to show the ray inside the block (1)
Model answer
Mark crosses on the incident ray and emergent ray, and where they meet the block. Remove the block, draw the incident and emergent rays, and join the entry point to the exit point to show the path inside.
Explain two precautions that make the measurements of the angles more accurate.
Mark scheme
use a narrow ray / thin slit (1); so the points can be placed more accurately (1); use a sharp pencil and a protractor with the centre on the point (1); to measure the angle accurately (1)
Model answer
Use a narrow ray, so the points marked are more accurate, and use a sharp pencil and place the protractor carefully to measure the angle.
A student measures an angle of incidence of 25° on a plane mirror. State the angle of reflection she should find and describe how she could check this.
Mark scheme
25° (1); mark the incident and reflected rays and remove the mirror (1); measure the angle between the reflected ray and the normal with a protractor (1)
Model answer
She should find 25°. She can mark the rays, remove the mirror, and measure the angle of reflection from the normal with a protractor.
The results table shows that when i = 60°, r = 35°. Explain what happens to the difference between i and r as i increases, and what this shows.
Mark scheme
the difference between i and r gets bigger as i increases (1); so the bending gets bigger at larger angles / angle of refraction is not proportional to the angle of incidence (1)
Model answer
The difference gets bigger as the angle of incidence increases (from 3° at 10° to 25° at 60°), so the angles are not directly proportional.
Describe an experiment to investigate how the angle of refraction depends on the angle of incidence for a glass block. Include safety precautions.
Mark scheme
draw round the block and draw a normal (1); use a ray box to direct a ray at the block at different angles of incidence (1); mark the entry and exit points and remove the block to draw the paths (1); measure the angles of incidence and refraction from the normal with a protractor (1); precaution: the ray box gets hot / do not look directly at the beam / use a darkened room (1)
Model answer
Draw round the glass block, draw a normal, and direct a ray from a ray box at different angles. Mark the ray in and out, remove the block, and join the points. Measure the angles of incidence and refraction from the normal with a protractor. The ray box gets hot, so it must not be touched, and the beam must not be looked into.
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