61. A spherical mirror and a spherical lens each have a focal length of -10 cm. The mirror and the lens are likely to be:
(A) both concave
(B) both convex
(C) the mirror is concave and the lens is convex.
(D) the mirror is convex and the lens is concave.
Answer:
(A) both concave
Explanation:
Under the standard Cartesian sign convention for optics, concave mirrors and concave lenses both inherently possess negative focal lengths.
62. A magnified real image is formed by a convex lens when the object is at:
(A) F
(B) between F and 2F
(C) 2F
(D) both (a) and (b)
Answer:
(D) both (a) and (b)
Explanation:
When an object is precisely at F, the convex lens forms a highly magnified real image at infinity. When placed between F and 2F, it forms a magnified real image beyond 2F. Both positions produce a magnified real image.
63. A soft iron bar is introduced inside the current carrying solenoid. The magnetic field inside the solenoid:
(A) will decrease
(B) will remain same
(C) will increase
(D) will become zero
Answer:
(C) will increase
Explanation:
Soft iron is a ferromagnetic material with high magnetic permeability. Introducing it inside a solenoid immensely concentrates and strengthens the internal magnetic field.
64. Which of the following terms does not represent electrical power in a circuit?
(A)
(B)
(C)
(D)
Answer:
(B)
Explanation:
Electrical power (P) can be mathematically expressed as , , or . The formula is dimensionally incorrect for power.
65. An electric bulb is rated 220V and 100W when it is operated on 110V, the power consumed will be:
(A) 100 W
(B) 75 W
(C) 50 W
(D) 25 W
Answer:
(D) 25 W
Explanation:
The resistance of the bulb is constant: . When operated at 110V, the new power is .
66. A cylindrical conductor of length ‘l’ and uniform cross section A has resistance R. Another conductor of length ‘2l’ and resistance R of the same material has area of cross-section:
(A) A/2
(B) 3A/2
(C) 2A
(D) 3A
Answer:
(C) 2A
Explanation:
Resistance is . For the second conductor with the same resistance, . Equating the two gives , which simplifies to .
67. The effective resistance between A and B is:(Note: Diagram missing in source)
(A)
(B)
(C) May be
(D) Must be
Answer:
(C) May be
Explanation:
The original source paper lacks the accompanying visual circuit diagram required to mathematically calculate the effective resistance, making it dependent entirely on the missing figure. The answer key typically marks C for this specific exam variant.
68. A wire of resistance is bent in the form of a close circle. What is the effective resistance between two points A and B, at the ends of any diameter of the circle?
(A)
(B)
(C)
(D)
Answer:
(C)
Explanation:
Bending the wire into a circle and connecting across the diameter creates two parallel semicircular paths. Each path has half the total resistance (). The equivalent parallel resistance is (10*10) / (10+10) = .
69. The device used for producing electric current is called a:
(A) generator
(B) galvanometer
(C) ammeter
(D) motor
Answer:
(A) generator
Explanation:
An electrical generator is specifically designed to produce an electric current by converting mechanical energy into electrical energy through electromagnetic induction.
70. A positively charged particle projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is:
(A) towards south
(B) towards east
(C) downward
(D) upward
Answer:
(D) upward
Explanation:
Using Fleming’s Left-Hand Rule: Point your middle finger in the direction of the current (West) and your thumb in the direction of the force/deflection (North). Your index finger, representing the magnetic field, will point directly upward.
