Physics (Part-ix) (Railway)

Total Questions: 50

41. When Blue light and Red light are mixed in equal amounts. they will produce light of colour: [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) White
(2) Cyan
(3) Yellow
(4) Magenta

Correct Answer: (4) Magenta
Note:

The secondary colors of light are those colors which are formed when two primary colors are mixed in equal amounts.

• Mixing red and blue light results in magenta light.

• Similarly, mixing blue and green light results in cyan light.

42. A light ray passing through the ________ of a lens passed without any deviation. [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) 2F (twice of focal length)
(2) Focus
(3) edges
(4) optical centre

Correct Answer: (4) optical centre
Note:

The ray passing through optical center does not deviate.

• This is because the curvature of the lens at the incident and exit point are exactly opposite.

43. The direction of the induced current when the conductor is moving in the region of magnetic field is given by: [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) Right-hand thumb rule
(2) Fleming's left-hand rule
(3) Fleming's right-hand rule
(4) Maxwell's corkscrew rule

Correct Answer: (3) Fleming's right-hand rule
Note:

Direction of current induced in a wire moving in a magnetic field is using Fleming's right-hand rule.

According to the rule, if we extend the fore finger, middle finger, and the thumb of our right hand perpendicular to each other as shown in the figure with the thumb pointing towards the motion of the conductor and the fore finger pointing towards the magnetic field direction, the middle finger gives us the direction of induced current flowing in the circuit.

44. If the length of a conductor is doubled and the area of cross section is halved the resistance will be__________. [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) eight times of its original value
(2) four times of its original value
(3) half of its original value
(4) unaltered

Correct Answer: (2) four times of its original value
Note:

Resistance when length is 1 and area is A is R1 =→ 1/A

• Now new length is 21 and area is A/2 so new resistance will be = R2 = →21/A/2 = 41/A = 4R1

45. In the following table, the direction of incident ray of light and the direction of reflected ray of light are given in two different columns: Choose the correct match of column I to column II. [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

Column I – Direction of ray of light before reflection	Column II – Direction or ray of light after reflection
(A) Incident ray passing through or directed on the principal focus	(P) Will pass through or appear to diverge from the principal focus
(B) Incident ray passing through or directed on the center of curvature	(Q) Reflected ray is on the other side of the principal axis making same angle with respect to the incident ray
(C) Incident ray passing parallel to principal axis	(R) Reflected ray propagate parallel to the principal axis
(D) Incident ray directed on to the pole of the mirror making an angle with the principal axis	(S) Reflected ray will retrace the path of incidence in the opposite direction

(1) A-P, B-S, C-9, D-R
(2) A-R, B-S, C-Q, D-P
(3) A-R, B-Q, C-P, D-S
(4) A-R, B-S, C-P, D-Q

Correct Answer: (4) A-R, B-S, C-P, D-Q
Note:

The correct matches are as follows:

Column I – Direction of ray of light before reflection	Column II – Direction or ray of light after reflection
(A) Incident ray passing through or directed on the principal focus	(R) Reflected ray propagate parallel to the principal axis
(B) Incident ray passing through or directed on the center of curvature	(S) Reflected ray will retrace the path of incidence in the opposite direction
(C) Incident ray passing parallel to principal axis	(P) Will pass through or appear to diverge from the principal focus
(D) Incident ray directed on to the pole of the mirror making an angle with the principal axis	(Q) Reflected ray is on the other side of the principal axis making same angle with respect to the incident ray

46. The compass needle gets deflected when it is brought near to a bar magnet because it________. [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) is a tiny magnet
(2) is a conductor
(3) carries current
(4) is an iron rod

Correct Answer: (1) is a tiny magnet
Note:

A compass needle gets deflected when brought near a bar magnet because a magnetic compass can be considered as a pole, and the magnet creates a field.

• The pointer on a compass acts as the north pole of a small magnet.

• If we place the two at rest, then the compass will be reflected in a direction, and it will be constant.

47. The unit Watt can be expressed as ________. [RRB Group 'D' CBT Exam, 06.10.2022 (Shift-II)]

(1) 1 Watt = 1 Volt/1 Ampere
(2) 1 Watt = 1 Volt x 1 Cou-lomb
(3) 1 Watt = 1 Volt x 1 Ampere
(4) 1 Watt =1 Volt/1 Coulomb

Correct Answer: (3) 1 Watt = 1 Volt x 1 Ampere
Note:

Watt is the rate at which electrical work is performed when a current of one ampere flows across the potential difference of one volt.

• The volt ampere is dimensionally equivalent to the watt.

• In SI units, 1 Watt = 1 Volt x 1 Ampere

48. The ratio of currents flowing through two electric circuits is 1: 4. If the ratio of resistances is 2:1, what is the ratio of their powers? [RRB Group 'D' CBT Exam, 07.10.2022 (Shift-I)]

(1) 32 :1
(2) 1 :8
(3) 8 :1
(4) 1 :32

Correct Answer: (2) 1 :8
Note:

P = I²

P1 = (1)² * 2 = 2

P2 = (4)² * 1 = 16

So, p1/p2

= 2/16

= 1/8 = 1 : 8

49. In an electric motor, the forces acting on the arms of the armature of the motor that are perpendicular to the direction of magnetic field are: [RRB Group 'D' CBT Exam, 07.10.2022 (Shift-I)]

(1) equal in magnitude and in the same direction
(2) equal in magnitude and opposite in direction
(3) unequal in magnitude and along same direction
(4) unequal in magnitude and in the opposite direction

Correct Answer: (2) equal in magnitude and opposite in direction
Note:

In an electric motor, the direction of the force on a current-carrying conductor in a magnetic field is determined by Fleming's left-hand rule.

• According to it, the direction of forces are opposite, and they are equal in magnitude.

50. The image produced by a concave mirror when an object is kept at the centre of the curvature of the mirror is: [RRB Group 'D' CBT Exam, 07.10.2022 (Shift-I)]

(1) virtual and erect
(2) real and inverted
(3) real and erect
(4) virtual and inverted

Correct Answer: (2) real and inverted
Note:

If an object is placed at centre of curvature of a concave mirror, light rays meet to form an image which is real, inverted and at the same size as that of the object.

• The image formed is not magnified.

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