Physics (Part-VIII) (Railway)

Total Questions: 50

31. A student measured the magnification of a spherical lens and a spherical mirror. He found that both are - 3.0. He would conclude that: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) the lens and the mirror both are convex
(2) the lens and the mirror both are concave
(3) the lens is convex but the mirror is concave
(4) the lens is concave but the mirror is convex

Correct Answer: (3) the lens is convex but the mirror is concave

Solution:Magnification of a concave lens or a convex mirror is always positive because they always form virtual and erect images.

• It can be negative or positive for a convex lens or a concave mirror.

• The magnification of an image by convex lens is positive only when the object is placed between focal point(F) and optical centre.

32. Name the physico-chemical process by which plants convert light energy into chemical energy. [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) Physico-chemical conversion
(2) Starch synthesis
(3) Photosynthesis
(4) Physical synthesis

Correct Answer: (3) Photosynthesis

Solution:Photosynthesis is a process by which green plants and certain other organisms synthesize their own food i.e.. transform sunlight energy into chemical energy with the help of chlorophyll, carbon dioxide and water.

• Chloroplast, found in plant cells, is the site of photosynthesis.

• It contains chlorophylls a and b that absorb visible light energy and convert it to usable chemical energy in photosynthesis.

33. In an electric circuit 2 lamps of resistances 10Ω and 20Ω are in parallel and a battery of 20V is applied. If power, voltage, current and resistance are represented by P, V, I and R, respectively, then which of the following relations holds true? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) P= V² R
(2) P = IR²
(3) P = V²/R
(4) P = V/R²

Correct Answer: (3) P = V²/R

Solution:P = I²R or

P = V²/R

34. A current of 15mA is flowing through an electronic device when the voltage across the device is 0.3 mV. The resistance of the device is: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-II)]

(1) 0.2 mΩ
(2) 20 mΩ
(3) 200 mΩ
(4) 2.0 mΩ

Correct Answer: (1) 0.2 mΩ

Solution:V= IR

R = V/I = 0.3/15 = 0.02 mΩ

35. The most essential difference between a DC and an AC generator is__________. [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) Higher Voltages are generated by AC generator Only
(2) DC generator uses a commutator and AC generator uses Slip rings
(3) DC generator has permanent magnet and AC has an electromagnet
(4) Higher voltages are generated by DC generator only

Correct Answer: (3) DC generator has permanent magnet and AC has an electromagnet

Solution:AC and DC Generators utilize electromagnetic induction to generate electricity.

• In AC generators we have slip rings whereas in DC generators we have commutators, whereas both can produce any given amount of voltage.

36. The sky appears blue due to: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) scattering of light of higher wave length
(2) scattering of light of lower wave length
(3) dispersion of light of higher wave length
(4) dispersion of light of lower wave length

Correct Answer: (2) scattering of light of lower wave length

Solution:The sky appears blue due to the scattering of light.

• Our atmosphere contains atoms and molecules of different sizes that scatter different wavelength of light.

• Since blue colour is scattered to the maximum extent by dust particles, the sky appears blue.

37. What is the heat energy pгоduced in a resistance of 10Ω when 5 A current flows through it for 5 minutes? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) 7.5 x 10⁵J
(2) 7.5 x 10⁶J
(3) 7.5 x 10³J
(4) 7.5 x 10⁴J

Correct Answer: (4) 7.5 x 10⁴J

Solution:Given

Resistane, R = 10Ω

current, I = 5 A

Time 5 min = 300s.

H = I² Rt

= (5)² * 10 * 300

= 75000

= 7.5 * 10⁴J

38. What is the unit of magnification? [RRB Group 'D' CBT Exam, 19.09.2022 39 (Shift-III)]

(1) cm
(2) Dioptre
(3) It has no unit
(4) Newton

Correct Answer: (3) It has no unit

Solution:Magnification is defined as the ratio of image height to object height.

• So, it has no unit because it is the measure of ratio and ratio has no unit representation.

39. If coil A of resistance 15Ω and coil B or resistance 5 Ω are subjected to time varying magnetic field, then the current induced in these coils are: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) in the ratio 1:1
(2) different
(3) in the ratio 1:2
(4) same

Correct Answer: (2) different

Solution:A time varying magnetic field induces a Voltage that is proportional to the rate of change of the wrrert producing it with a Positive value indicating an increase in emf and a negative value indicling a decrease in emf.

40. When an object is placed at a point 21 cm in front of a convex mirror, the image is formed at 7 cm behind the mirror. Now, someone moves the object to a distance of 14 cm in front of the mirror. The distance of the image from the mirror (in cm) now is: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) +3
(2) -6
(3) +6
(4) -3

Correct Answer: (3) +6

Solution:1/f = 1/u + 1/v = 1/- 21 + 1/7

= 7 - 21/21 * 7 = 2/21

u = - 14 cm

2/21 = - 1/14 + 1/V

1/V = 2/21 + 1/14

= 28 + 21/21 * 14 = 49/294 = 1/6

V = +6 cm

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