Parallel rays meeting a convex lens converge at its principal focus, and a convex lens is also called a converging lens, so this Year 10 sheet opens by naming the focus and the lens. A virtual image answer and the focal length both appear in the key.
Key Takeaways
A convex lens converges parallel rays at the principal focus (Q1).
A convex lens is also called a converging lens (Q2).
Q3 records a virtual image among the answers.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.A convex lens converges parallel rays of light to a point called the
(a) principal focus(b) centre of curvature(c) pole(d) vertex
(a) a virtual image(b) a real image(c) an enlarged image(d) no image at all
4.The distance between the centre of a lens and its principal focus is the
(a) focal length(b) radius of curvature(c) object distance(d) image distance
5.In a camera, the image formed on the film or sensor is
(a) real and inverted(b) virtual and upright(c) virtual and inverted(d) real and upright
6.A magnifying glass uses
(a) a convex lens(b) a concave lens(c) a plane mirror(d) a prism
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.What is the principal focus of a convex lens?
8.Define focal length.
9.What type of image does a concave lens always form?
10.Give one use of a convex lens and one use of a concave lens.
11.Write the lens formula.
12.Where must an object be placed in front of a convex lens to obtain a virtual, magnified image?
13.What is the power of a lens and what is its unit?
14.How do concave lenses correct short sight (myopia)?
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A convex lens of focal length 10 cm has an object placed at 30 cm from it. Using 1/v = 1/f − 1/u with u = −30 cm and f = +10 cm, find the image distance.
16.A lens has a focal length of 25 cm. Using power = 1 ÷ f (with f in metres), find its power.
17.A lens has a power of −2 D. Using f = 1 ÷ power, find its focal length in metres.
18.An object is placed at 20 cm from a convex lens of focal length 10 cm. Using 1/v = 1/f − 1/u with u = −20 cm and f = +10 cm, find the image distance.
19.A concave lens of focal length 15 cm has an object placed 30 cm in front of it. Using the lens formula with f = −15 cm and u = −30 cm, find the image distance.
20.A convex lens has a focal length of 50 cm. Convert this to metres and then find the power of the lens.
Answer Key
1. a) principal focus
2. a) converging lens
3. a) a virtual image
4. a) focal length
5. a) real and inverted
6. a) a convex lens
7. Refer to solution guide.
8. Refer to solution guide.
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20. Refer to solution guide.
End of Worksheet
People Also Ask
Where do parallel rays converge after a convex lens?
At the principal focus, option (a) in this worksheet (Q1).
What else is a convex lens called?
A converging lens, option (a) in this worksheet (Q2).
What kind of image is formed when an object is between the lens and its focal point?
A virtual image, option (a) in this worksheet (Q3).
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