AQA GCSE Physics Physics Paper 2 (Higher), November 2021: Question 4
10 marks · Standard Demand difficulty · Short Answer
Describe concave and convex lens images, complete a convex lens ray diagram, analyze image distance graphs and calculate measurement uncertainty, and explain why a blue object appears black under red light.
Practise this questionQuestion
Question text
04 Lenses are used to form images of objects.
04.1 Figure 6 shows how a concave lens forms an image of an object.
Figure 6
The image of the object in Figure 6 is upright.
Give two other words that describe the image.
[1 mark]
04.2 Figure 7 shows an object near to a convex lens.
Complete the ray diagram to show how the image is formed.
Use an arrow to represent the image.
[3 marks]
Figure 7
The position of an image formed by a convex lens varies with the distance between
the object and the lens.
Figure 8 shows the results of a student’s investigation using a convex lens.
Figure 8
04.3 Describe how the distance of the image from the lens decreases as the distance
between the object and the lens increases.
[1 mark]
04.4 The student measured the distance from the image to the lens four times.
The distance between the object and the lens did not change.
The 4 measurements from the image to the lens were:
1.9 cm 1.7 cm 2.2 cm 1.4 cm
Calculate the uncertainty in the measurements.
[2 marks]
Uncertainty = ± cm
04.5 Figure 9 shows a spotlight containing a convex lens.
A red filter is placed in front of the spotlight.
The spotlight is directed at a blue object.
Figure 9
Explain why the blue object appears black.
[3 marks]
Mark scheme
Show the mark scheme
Question 4
AO/
Question Answers Extra information Mark
Spec. Ref
04.1 both answers correct answers may be in either order 1 AO3
4.6.2.5
virtual
diminished allow a description of diminished
(eg smaller / reduced)
04.2 any two correct lines drawn allow construction lines that are 2 AO2
from the top of the object, not dashed 4.6.2.5
passing through the lens and allow 1 mark for two correct
traced backwards lines drawn from the top of the
object, passing through the lens
BUT not traced backwards
image drawn in the correct mark only scores if first two
position and with the correct marks score
orientation
04.3 (increasing the object distance) do not accept inversely 1 AO3
decreases the image distance proportional 4.6.2.5
more rapidly at small (object)
distances / more gradually at
larger (object) distances
04.4 (2.2 – 1.4) 1 AO3
2 4.6.2.5
uncertainty = (±) 0.4 (cm) 1
allow
1.9 + 1.7 + 2.2+ 1.4 = 1.8 (1)
(2.2 – 1.8 = ) (±) 0.4 (cm) (1)
04.5 only red is transmitted by the 1 AO1
filter 4.6.2.6
red is absorbed by the (blue) 1
object
(so) no light is reflected by the 1
(blue) object
Total 10
How to answer it
Study Guide: Lenses and Wave Properties
This question assesses your understanding of ray diagrams for concave and convex lenses, describing relationships from graphs, calculating experimental uncertainty, and applying knowledge of colour filters and light absorption/reflection.
Part 04.1: Describing Lens Images
Spec reference: 4.6.2.5
✅ Correct Answer
- Virtual
- Diminished (or smaller / reduced)
💡 Key Knowledge
- A concave lens (diverging lens) always produces an image that is upright, virtual (formed where diverging rays appear to come from), and diminished (smaller than the object).
🧠 Exam Technique
Both words must be correct to secure the single mark. Make sure you learn the standard trio of descriptors for lens images: magnified/diminished, real/virtual, and upright/inverted.
Part 04.2: Convex Lens Ray Diagram
Spec reference: 4.6.2.5
✅ Correct Answer
- Two correct construction lines drawn from the top of the object passing through the lens and traced backwards to form the image.
- Image drawn upright, virtual, and larger (magnified) at the correct position behind the lens.
💡 Key Knowledge
- When an object is placed closer to a convex lens than its focal length (F), it acts as a magnifying glass.
- Rays diverge through the lens and must be extended backward using dashed lines to locate the virtual image.
🧠 Exam Technique
Use a sharp pencil and a ruler! Draw at least two standard rays: one parallel to the axis then refracting through the far focal point, and one passing straight through the optical centre. Trace refracted rays backwards with dashed lines.
❌ Common Errors
Students often forget to trace the diverging rays backwards with dashed lines on the left side of the lens, losing marks for the image location.
Part 04.3: Interpreting Graph Trends
Spec reference: 4.6.2.5
✅ Correct Answer
As object distance increases, image distance decreases more rapidly at small distances and more gradually at larger distances.
🧠 Exam Technique
Look closely at the gradient (steepness) of the curve. Examiners explicitly note: do not accept "inversely proportional"—you must describe the changing rate of decrease shown by the curve shape.
Part 04.4: Calculating Uncertainty
Spec reference: 4.6.2.5
📐 Step-by-Step Calculation
- Find mean (if not using range directly):
Mean = (1.9 + 1.7 + 2.2 + 1.4) / 4 = 1.8 cm - Calculate uncertainty using half the range:
Uncertainty = (Maximum value − Minimum value) / 2
Uncertainty = (2.2 − 1.4) / 2 = 0.4 cm
✅ Final Answer
Uncertainty = ± 0.4 cm
❌ Common Calculation Traps
Forgetting to divide the range by 2 is the most common error. Uncertainty is defined as plus-or-minus half the range of repeated measurements.
Part 04.5: Colour Filters and Reflection
Spec reference: 4.6.2.6
✅ Correct Answer
- Only red light is transmitted by the red filter.
- Red light is absorbed by the blue object.
- Therefore, no light is reflected by the blue object into the observer's eye, making it appear black.
💡 Key Knowledge
- Filters work by absorbing certain wavelengths and transmitting others. A red filter only transmits red light.
- Colored objects absorb specific wavelengths of light corresponding to their complementary colors and reflect their own color. A blue object absorbs red and green light, reflecting blue.
🧠 Exam Technique
Structure your answer sequentially: 1) What light passes the filter? 2) What happens to that light when it hits the object? 3) What reaches the eye?
Topics
Physics · P6: Waves
Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 2 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.