61) The angle of vision for a healthy human being is about:
A) \( 90^\circ \)
B) \( 180^\circ \)
C) \( 120^\circ \)
D) \( 60^\circ \)
62) What do the cones in our eyes identify?
A) Shape and size of objects
B) Light and dark contrast
C) Color
D) Motion and depth
63) Which of the following works on the principle of electromagnetic induction?
A) Electric fan
B) Transformer
C) Electric heater
D) All of the above
64) Which of the following is the lens maker's formula?
A) \( \frac{1}{f} = \left( \frac{1}{v} – \frac{1}{u} \right) \)
B) \( \frac{1}{f} = \left( \mu – 1 \right) \left( \frac{1}{R_1} – \frac{1}{R_2} \right) \)
C) \( f = \mu \left( R_1 + R_2 \right) \)
D) \( f = \left( \mu + 1 \right) \left( \frac{R_1 + R_2}{2} \right) \)
65) The focal plane of a lens is a plane:
A) Parallel to the principal axis at the focus
B) Perpendicular to the lens
C) At a fixed distance from the lens
D) At the focal point of the lens
66) A prism is made with refractive index \( \mu = 2 \) and angle 60°. The angle of minimum deviation is:
A) \( 30^\circ \)
B) \( 45^\circ \)
C) \( 60^\circ \)
D) \( 90^\circ \)
67) When a convex lens is placed in water, its focal length:
A) Increases
B) Decreases
C) Remains constant
D) Becomes infinite
68) A watch repairer uses a magnifying glass. Which lens is used?
A) Concave lens
B) Convex lens
C) Plane mirror
D) Concave mirror
69) An air bubble in water behaves like:
A) A concave lens
B) A convex lens
C) A plane mirror
D) A diverging lens
70) The shape of magnetic field lines around a straight current-carrying wire is:
A) Circular
B) Elliptical
C) Radial
D) Straight lines
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