Physicsmedium · Past Paper
Calculate the focal length of a convex lens which forms a real image at 20 cm when an object is placed 20 cm away.
A20 cm
B10 cm
C40 cm
D5 cm
✓ Correct Answer: B — 10 cm
Using 1/f = 1/v - 1/u: 1/f = 1/20 - 1/(-20) = 1/20 + 1/20 = 2/20 = 1/10. So, f = 10 cm.
Share this question
More from Physics
- Which of the following is a non-renewable source of energy?
- If the radius of Earth was double its present value, and its mass remained the same, what would be the weight of a 60 kg person?
- What is the speed of sound in water at 20 degrees Celsius?
- If the distance between two masses is tripled, the gravitational force becomes:
- Which instrument is used to measure electric current in a circuit?