Physics (Part-IV) (Railway)

Total Questions: 50

41. A given resistance R is cut into 2 equal parts. The resistance of each pair is: [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-II)]

(1) 2 R
(2) R/4
(3) R
(4) R/2

Correct Answer: (4) R/2

Solution:We know that total resistance = R

• So, when the resistance is cut into two equal parts. Hence, the resistance of each part is now ½ of the original Resistance, i.e. R/2

42. The potential drop across the 4Ω resistor in the given circuit is: [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-II)]

(1) 5 V
(2) 3 V
(3) 2 V
(4) 0.5 V

Correct Answer: (3) 2 V

Solution:We are provided with a circuit which has resistances and voltage connected to it as an electrical component. 4Ω and 6Ω are connected in series with a voltage of 5V.

• Total resistance in Series 4Ω + 6Ω = 10Ω

• So, the current flowing through circuit I = V/R = 5/10 = 0.5A

• The voltage remains the same across all the components. Therefore, potential drop against the resistance 4Ω is given as V = IR = 0.5 * 4 = 2 volts

• Hence, the potential drop across the 4Ω resistance is 2V

43. The distance between the pole and centre of curvature of a spherical mirror, in terms of its focal length f, is equal to [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-II)]

(1) f/2
(2) 2f
(3) f
(4) f/4

Correct Answer: (2) 2f

Solution:Pole is a point on the spherical mirroг.

• Centre of curvature is the centre of the sphere of which the mirror forms a part.

• Hence, the distance between them is the radius of curvature.

• Focal length (f) and radius of curvature (R) are related as: f = R/2

• So, R = 2f

44. The resistivity of a material is dependent on which of the following factors? [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(1) Resistance
(2) Area of cross section
(3) Length
(4) Temperature

Correct Answer: (4) Temperature

Solution:Resistivity is the nature of a material that allows or resists the flow of electric current through a given element or material.

• The resistivity of materials depends on the temperature as Pt =P₀ [ 1 + α (T - T₀), where p₀ is the resistivity at a standard temperature, pt is the resistivity at to C. T₀, is the reference temperature, and a is the temperature coefficient of the resistivity.

• Resistivity is indirectiv proportional to the temperature. In other words, as we increase the temperature of materials, their resistivities will decrease.

45. Which of the following rules Is used to determine the direction of induced current due to the motion of coil at right angle to the magnetic field? [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

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

Correct Answer: (4) Fleming's right-hand rule

Solution:Fleming's Right-hand rule is used to determine the direction of induced current due to the motion of coil at right angle to the magnetic field.

• Fleming's Right Hand Rule states that if we arrange our thumb, forefinger, and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the motion of the conductor relative to the magnetic field. the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the induced current.

46. A convex mirror used as a rearview mirror of a car has a focal length of 2m. If a bus is located at a distance of 3m from the mirror, where will its image be formed? [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(1) 0.83 m in front of the mirror
(2) 1.2 m in front of the mirгог
(3) 0.83 m behind the mirror
(4) 1.2m behind the mirror

Correct Answer: (4) 1.2m behind the mirror

Solution:From the Mirror formula, we know that 1/f = 1/v + 1/u

According to the question, f= 2m and u= -3m

So, 1/2 = 1/v + 1/-3

Or 1/v = ½ +1/3 = 5/6

∴v=6/5= 1.2 m

Therefore, the image is formed 1.2 m behind the mirror.

47. The bluish colour of water in deep sea is due to: [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(1) scattering of light
(2) refraction of light
(3) dispersion of light
(4) reflection of light

Correct Answer: (1) scattering of light

Solution:Water molecules absorb sunlight and scatter the different colours.

• Colours having longer wave length can be absorbed easily whereas colors with lesser wavelengths will be scattered.

• Red, orange, yellow, and green having longer wavelengths are absorbed by water molecules quickly when sunlight hits water, while colors with shorter wavelengths such as blue and violet are scattered.

• So, blue colour of deep sea is mainly due to scattering of light.

48. Which of the following is the commercial unit of electric energy? [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(1) Kilowatt hour
(2) Joule
(3) Calorie
(4) watt second

Correct Answer: (1) Kilowatt hour

Solution:Commercial unit of electrical energy is kWh (kilowatt-hour).

• It is defined as energy consumed by an appliance of 1kW when it is used for one hour.

49. Which of the following situations is/are possible ? [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(a) Magnetic field line can be parallel to each other.

(b) Magnetic field lines can be concentric circles.

(1) Only (b)
(2) Both (a) and (b)
(3) Both (a) and (c)
(4) Only (a)

Correct Answer: (2) Both (a) and (b)

Solution:Magnetic field lines can be parallel to each.

• If the field lines in a magnetic field are parallel and equidistant, the magnetic field is uniform.

• The magnetic field lines around a straight current carrying conductor are in form of concentric circles.

50. A ray of light is incident on an interface separating two media along the normal to the Interface. The angle between the incident ray and refracted ray is eqwal to: [RRB Group 'D' CBT Exam, 17.08.2022 (Shift-III)]

(1) 0°
(2) 45°
(3) 90°
(4) 30°

Correct Answer: (1) 0°

Solution:If Incident ray is normal to interface then i = 0 as the angle is measured with respect to the normal.

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