Physics (Part-V) (Railway)

Total Questions: 50

21. The speed of light in two transparent mediaum A and B are 2 * 10⁸ m/sec and 2.25 * 10⁸ m/sec. The refractive index of medium A with respect to medium B is equal to: [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) 1.125
(2) 4.50
(3) 0.89
(4) 4.25

Correct Answer: (1) 1.125

Solution:Refractive index of medium A with respect to medium B= speed of light in medium B/speed of light in medium A

• So, according to the question. Refractive index of medium A with respect to medium B = (2.25 x 10⁸ m/sec)/(2 x 10⁸ m/sec) = 1.125

22. A metallic wire of resistance 100Ω is bent into a circle having cirecumference equal to the length of the wire. The equivalent resistance between two diametrically opposite points of the circle is: [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) 75 Ω
(2) 50 Ω
(3) 100 Ω
(4) 25 Ω

Correct Answer: (4) 25 Ω

Solution:When a wire is bent to form a circle, it is equivalent to two resistor wires connected in parallel across the diametrically opposite points.

• If L is the initial length of the wire, on bending it forms two wires of length L/2.

• R α 1. Therefore, the resistances of the two half-length wires will be R/2 each.

• The resistance across any two diametrically opposite points = equivalent resistance in parallel. ⇒ R = R/4

• So, according to the question. the equivalentresistance between two diametrically opposite points of the circle = R/4 = 100/4 = 25Ω

23. A concave mirror forms a real, inverted and same size image of an object. Where is the object placed? [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) Between f and pole
(2) At infinity
(3) Between f and C
(4) At C

Correct Answer: (4) At C

Solution:If an object is at the centre of curvature of a concave mirror, then the image is formed at the same position and will be real, inverted and of the same size.

• The image is formed at the same distance from the mirror as the object.

24. To investigate the conduction of electric current, Ravi performed an experiment. He took different aqueous solutions or liquids (as electrolyte) and tried to pass electricity and connected the circuit with a bulb. In the presence of which of the following, will the bulb NOT glow? [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) Octane (ʅ)
(2) Copper sulphate (aq)
(3) Sodium chloride(aq)
(4) Calcium chloride (aq)

Correct Answer: (1) Octane (ʅ)

Solution:Octane (ʅ)

• Electrical conductivity is based on the flow of electrons.

• Strong acids and salts are strong electrolytes because they completely ionize (dissoclate or separate) in solution.

• The ions carry the electric charge through the solution thus creating an electric current.

• Soluble Salts such as Sodium Chloride, Copper Sulphate or Calcium Chloride are strong electrolytes and thus bulb will glow in their presence.

25. The ratio of the field due to a current carrying circular coil of n turns to the field due to a single circular loop of same radius carrying the same current is_______. [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) 1 : n²
(2) n : 1
(3) 1 : n
(4) 1 :1

Correct Answer: (2) n : 1

Solution:• The magnetic field produced by a Current carryerg wire at a given point depends directly on the current passing through it.

• Therefore if ther is a circular coll gavumg 'n' turns, the field priduced is'n' times as large as that produced by a deingle turn.

• This is because the currect in each circulas turn has the dame direction, and the field due to each turn then just adds up.

26. What is the process of generating current induced by a change in magnetic field called? [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-I)]

(1) Electromagnetism
(2) Electromagnetic induction
(3) Electric conduction
(4) Electromagnetic radiation

Correct Answer: (2) Electromagnetic induction

Solution:The phenomenon in which electric current is generated by varying magnetic fields is appropriately called electromagnetic induction.

• This either happens when a conductor is placed in a moving magnetic field (when using an AC power source) or when a conductor is constantly moving in a stationary magnetic field.

• Electromagnetic Induction was discovered by Michael Faraday in 1831.

27. The direction of a magnetic field due to a straight current carrying conductor can be determined using: [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-II)]

(1) Fleming's left-hand rule right hand rule
(2) right hand thumb rule
(3) fleming's right-hand rule
(4) left hand thumb rule

Correct Answer: (2) right hand thumb rule

Solution:The Magnetic field lines around a straight conductor carrying current are concentric circles whose centres lie on the wire.

• The direction of these magnetic field lines can be determined using Right-Hand Thumb Rule.

28. A light ray AB is incident on a convex mirror as shown in the figure. What will be the angle of reflection? [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-II)]

(1) 0°
(2) 30°
(3) 90°
(4) 45°

Correct Answer: (1) 0°

Solution:When a ray is directed in the direction of the centre of curvature of a convex mirror the rays will be reflected along same path.

• So, the angle of reflection will be 0º.

• This occurs because the incident rays fall on the mirroг along the normal to the reflecting surface.

29. The resistance of a conductor is directly proportional to: [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-II)]

(1) area of cross section of the conductor
(2) length of the conductor
(3) potential difference applied across the conductor
(4) current flowing through the conductor

Correct Answer: (2) length of the conductor

Solution:Resistance is directly proportional to the length of the conductor.

• So, as the length increases, the magnitude of resistance Increases.

30. Which of the following devices is/are based on heating effect of electric current? [RRB Group 'D' CBT Exam, 22.08.2022 (Shift-II)]

(i) Incandescent lamp

(ii) Electric geyser

(iii) Electric generator

(1) Only (i)
(2) Both (i) and (ii)
(3) Only (ii)
(4) Both (i) and (iii)

Correct Answer: (1) Only (i)

Solution:When an electric current is passed through a conductor, it generates heat due to the hindrance caused by the conductor to the flowing current.

• The work done in overcoming the hindrance to the current generates heat in that conductor.

• The heating effect of electric current is widely used in electric iron, kettle, Incandescent lamp, geyser, toaster, heater, electric fuse, etc.

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