Sec 4 Physics Thin Converging Lenses topical questions

Define the principal focus and the focal length of a thin converging lens.

State the paths of the three standard construction rays used in lens ray diagrams.

An object stands 30 cm from a converging lens whose focal length is 10 cm. State the nature and approximate position of the image.

Explain why a virtual image cannot be caught on a screen.

A lens forms a 6.0 cm image of a 1.5 cm object, with the image 40 cm from the lens. Calculate the linear magnification and the object distance.

A student photographs a 1.7 m friend, and the sensor image is 3.4 mm tall with the sensor 5.0 cm behind the lens.

1. (a)Calculate the linear magnification.[2]
2. (b)Calculate how far the friend stood from the lens.[2]
3. (c)State the nature of the image on the sensor.[2]

A projector uses a slide 24 mm wide and throws a picture 1.2 m wide. The slide sits 8.0 cm from the lens.

1. (a)Calculate the linear magnification.[2]
2. (b)Calculate the lens-to-screen distance.[2]
3. (c)Explain why the slide is inserted upside down.[2]

A converging lens of focal length 4.0 cm has an object 12 cm away (drawn to scale, 1 cm : 2 cm).

1. (a)State which two construction rays you would draw.[2]
2. (b)The rays cross 6.0 cm beyond the lens. Describe the image.[2]
3. (c)Calculate the image height for a 4.0 cm object.[2]

A jeweller inspects a gem through a lens of focal length 5.0 cm, holding the gem 3.0 cm from the lens.

1. (a)State the nature of the image seen.[2]
2. (b)Explain, using rays, why the image is virtual.[2]
3. (c)State and explain which of two lenses (f = 5.0 cm or f = 15 cm) allows closer, larger viewing.[2]

Three optical devices each use a single converging lens: a camera (tree 15 m away), a projector (slide just outside f) and a magnifying glass (stamp inside f).

1. (a)Copy and complete: state the nature of the image in each device (real/virtual, upright/inverted, magnified/diminished).[6]
2. (b)State the one condition shared by the camera and the projector but not the magnifying glass.[2]

A student measures the focal length of a converging lens by forming a sharp image of a window on paper, then checks with an object at 30 cm that forms its image at 15 cm.

1. (a)Explain why the paper must be placed at the principal focus when the window is very distant.[3]
2. (b)For the check: state the object distance, image distance and describe the image.[3]
3. (c)A 4.0 cm object is used in the check. Show that the magnification from distances agrees with the heights if the image measures 2.0 cm.[2]

A student covers the top half of a converging lens with thick paper while a real image stands on a screen.

1. (a)State what happens to the image on the screen.[2]
2. (b)Explain the result using ray reasoning.[4]
3. (c)State one everyday situation where the same reasoning applies.[2]

A stamp collector wants a magnifier giving a large clear view. Two lenses are available: f = 4.0 cm (thick, short) and f = 20 cm (thin, long).

1. (a)State the object position needed for either lens to act as a magnifier.[2]
2. (b)Explain which lens gives the larger view of tiny detail and why.[4]
3. (c)State one disadvantage of the chosen lens for a collector with an unsteady hand.[2]