Physics (Part-VII) (Railway)

Total Questions: 50

41. The path of a ray of light incident on an interface separating two transparent media is shown in the figure. The refractive index (n) of medium B with respect to medium A is given by: [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) 0<n<1
(2) n = 1
(3) n > 1
(4) n = 0

Correct Answer: (3) n > 1

Solution:The refractive index of second medium with respect to first medium is defined as the ratio of the sine of angle of incidence in the first medium to the sine of the angle of refraction in the second medium.

• Refractive index (n) of a medium is always greater than 1 (n >1) it cannot be less than 1 because the speed of light in any medium is always less than that in vacuum.

42. Conversion of energy in electric motor is: [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) Mechanical energy to electrical energy
(2) Electrical energy to heat energy
(3) Electrical energy to mechanical energy
(4) Sunlight to electrical energy

Correct Answer: (3) Electrical energy to mechanical energy

Solution:An electric motor is an electrical machine that converts electrical energy into mechanical energy.

• It works on the principle of the current carrying conductor which creates the magnetic field around itself.

• Mechanical energy is that energy that is owned by an object due to the motion or because of their position. Electrical energy is due to the moving of the electric charges.

43. If an object is placed 36 cm in front of a concave mirror of focal length 18 cm, then its image will be formed_________. [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) at 36 cm in front of the mirror
(2) at 18 cm behind the mirгог
(3) at 18 cm in front of the mirror
(4) at 36 cm behind the mirгог

Correct Answer: (1) at 36 cm in front of the mirror

Solution:at 36 cm in front of the mirror According to the question, f= -18 cm, u=-36 From the mirror formula, we know 1/v+1/u=1/f Or 1/v + 1/-36=1/-18 Or 1/v = 1/-18 + 1/36= -1/36→ v = -36 cm The image is formed at a distance of 36 cm

44. If the number of turns in a solenoid increases, then: [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) magnetic field increases
(2) magnetic field decreases to zero
(3) magnetic field remains constant
(4) magnetic field decreases

Correct Answer: (1) magnetic field increases

Solution:The magnetic field inside a solenoid is directly proportional to both the applied current and the number of turns per unit length.

• Hence as the number of turns increases, the magnetic field also increases.

45. What happens when a pencil is immersed in water? [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) Pencil appears bent
(2) Colour of pencil changes
(3) Pencil looks curved
(4) Pencil appears bright

Correct Answer: (1) Pencil appears bent

Solution:When a pencil is dipped in water in a container, rays of light from the tip of the pencil bend away from the normal as they go from water to air.

• It because of the refraction of light.

46. An electric transformer works on the principle of: [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) Ohm's law
(2) photoelectric effect
(3) Joule's heating effect
(4) electromagnetic induction

Correct Answer: (4) electromagnetic induction

Solution:A transformer basically is very simple static electromagnetic passive electrical device tha tworks on the principles of "electromagnetic induction" as a mutual induction.

• Mutual induction is the process by which a coil of wire magnetically induces a voltage in another closely located coil.

• It converts electrical energy from one value to another by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself.

47. If a toaster is connected to 440 V AC instead of 220 V AC, then the heat produced per second will be___________ of the initial amount. [RRB Group 'D' CBT Exam, 14.09.2022 (Shift-II)]

(1) four times
(2) twice
(3) one-fourth
(4) half

Correct Answer: (1) four times

Solution:V x V²

V₁ = 440V

V₂ = 220V

= P₂/P₁ = Vz/V₁ ⇒ Pz/P₁ = 4P₁

48. The magnetic field produced by the long solenoid carrying current is: [RRB Group 'D' CBT Exam, 15.09.2022 (Shift-III)]

(1) maximum at the ends of the solenoid
(2) non-uniform inside the solenoid
(3) zero inside the solenoid
(4) uniform inside the solenoid

Correct Answer: (4) uniform inside the solenoid

Solution:The magnetic field inside a long straight solenoid carrying current is the same at all points.

• One end of the solenoid basically acts as a magnetic north pole whereas the other acts as a magnetic south pole.

• The field lines inside the solenoid are known to be parallel and straight.

49. Electric power consumed by two electric bulbs (each with 5Ω resistance) connected in series with a 3 V battery is: [RRB Group 'D' CBT Exam, 15.09.2022 (Shift-III)]

(1) 0.9 W
(2) 3 W
(3) 1 W
(4) 0.3 W

Correct Answer: (1) 0.9 W

Solution:The relationship between Power and Resistance can be expressed as:

• P= V²/R, where P is the Power and we measure it in watts or W, R is the resistance measured in ohms (Ω), and V = the potential difference applied across the ends of the conductor and is measured in Volts or simply V.

• According to the question.

two bulbs of 5Ω resistance each are connected in series.

• So, R=R1+R2=5+5=10Ω

• So, P=32/10 = 9/10 = 0.9 watt

50. An incident ray passes through the focus of a concave mirror. The reflected ray: [RRB Group 'D' CBT Exam, 15.09.2022 (Shift-III)]

(1) is parallel to the principal axis
(2) passes through the centre of curvature
(3) passes through the focus of the mirror
(4) is normal to the mirror

Correct Answer: (1) is parallel to the principal axis

Solution:Any incident ray starting or passing through the focus of a concave mirror travels parallel to the principal axis of the mirror after reflection.

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