Physics 5054 · O Level · Thin lenses

Thin lenses — practice question

A student determines the focal length of a convex lens. He assembles the apparatus shown in Fig. 2.1. He positions the lens some distance from the illuminated object. He slides the screen until a clear image of the object is formed on the screen.
(a(i))[2]

Measure the lengths $x$ and $y$ on Fig. 2.1 to the nearest millimetre. $x$ = [BLANK] cm $y$ = [BLANK] cm

(a(ii))[1]

Fig. 2.1 is drawn one-eighth full size. Calculate the distance $u$ from the object to the lens and the distance $v$ from the image to the lens. $u$ = [BLANK] cm $v$ = [BLANK] cm

(b)[2]

Calculate the focal length $f$ of the lens, by using the equation $f = \frac{uv}{(u+v)}$ Write your answer to 2 significant figures. $f$ = [BLANK] cm

(c)[1]

State one precaution that the student follows to obtain an accurate value for the focal length $f$ of the lens.

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This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “x is 2.6 cm” …

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