Physics (Part-VII) (Railway)

Total Questions: 50

1. The refractive indices of mediums 1, 2 and 3 are 1.46, 1.65 and 1.31, respectively. If the speed of light in the mediums are v₁, v₂ and v₃. respectively, which of the following relations between them is correct? [RRB Group 'D' CBT Exam, 30.08.2022 (Shift-I)]

(1) V₂ >V₃ >V₁
(2) V₃>V₁>V₂
(3) V₁=V₂=V₃
(4) V₁>V₂>V₃

Correct Answer: (2) V₃>V₁>V₂

Solution:The refractive index of a medium can be calculated using the following formula = c/v, where n is the refractive index of the medium, c is the velocity of light in vacuum, and v is the velocity of light in the medium

• From the equation n = c/v, we know that the refractive index of a medium is inversely proportional to the velocity of light in that medium. So, lower the refractive index, higher will be its speed in light and vice versa.

• Hence, V₃ > V₁> V₂

2. The refractive indices of ice and glass are 1.31 and 1.52, respectively. A ray of light passes from ice to glass. The refractive index of glass with respect to ice is__ and the ray bends _ the normal in glass. [RRB Group 'D' CBT Exam, 30.08.2022 (Shift-I)]

(1) 1.16, away from
(2) 0.86. away from
(3) 1.16 towards
(4) 0.86, towards

Correct Answer: (3) 1.16 towards

Solution:R.I of Ice = 1.31

R.I of glass = 1.52

R.I of grass with respect to ice = 1.52 /1.31 = 1.16

3. The focus of a concave mirror is at a distance of 16 cm from its pole. Its centre of curvature will be at a distance' of _______ from the pole. [RRB Group 'D' CBT Exam, 30.08.2022 (Shift-I)]

(1) 16 cm
(2) 24 cm
(3) 32 cm
(4) 8 cm

Correct Answer: (3) 32 cm

Solution:The distance between the pole and centre of curvature of a spherical mirror is called radius of curvature.

• The relation between radius of curvature and focal length of a spherical mirror is R = 2f, where R = radius of curvature of the lens and f = focal length of the lens

• So, according to the question R = 2 x 16 = 32 cm

4. According to mirror formula, the focal length of spherical mirror is equal to: [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

(1) uv/u-v
(2) uv/u+v
(3) u-v/uv
(4) u+v/uv

Correct Answer: (2) uv/u+v

Solution:For a spherical mirror, u is distance of object from pole, v is distance of image from pole, and f is focal length of mirror.

• From mirror formula, we get 1/f= 1/u+1/v=u+v/uv

• So, f= uv/u + v

5. A bulb filament is made of a _metal with_ melting point. [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

(1) strong, high
(2) strong, low
(3) weak, low
(4) weak, high

Correct Answer: (1) strong, high

Solution:The filament of a light bulb is made of a strong metal with high melting point such as Tungsten.

• Tungsten (Symbol W) is used to make the filament of an electric bulb because it has the highest melting point, lowest vapour pressure, and greatest tensile strength of any metal.

• It can reach high temperatures before melting as a result of these.

6. Consider the following statements about magnetic field due to a current-carrying solenoid: [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

(a) The magnetic field inside the solenoid is in the form of parallel straight lines.

(b) The strong magnetic field produced inside the solenoid can be used to magnetise a piece of a magnetic material.

Which of the above statements is/are correct?

(1) Only (a)
(2) Neither (a) nor (b)
(3) Both (a) and (b)
(4) Only (b)

Correct Answer: (3) Both (a) and (b)

Solution:The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid.

• A strong magnetic field produced inside a current carrying solenoid can be used to magnetize a piece of magnetic material like soft iron, by placing it inside the coil/solenoid.

• The magnet so formed is called an electromagnet.

7. A converging lens having focal length 50cm is kept in contact with a diverging lens having focal length 20cm. The power of combinaion of the two lenses is: [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

(1) +3D
(2) 8D
(3)-3D
(4)-8D

Correct Answer: (3)-3D

Solution:∴ p₁ = 100/50 = +2D

P₂ = 100/-20 = -5D

Peq = 2-5 = -3D

8. A steady current I flows through an appliance of resistane R. The amount of heat produced by it in time t is: [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

(1) (I² t)/R
(2) I²Rt
(3) (lt)/R
(4) IRt

Correct Answer: (2) I²Rt

Solution:The heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I²Rt.

• This equation is called the Joule's equation of electrical heating.

9. Which of the following devices is NOT based on the concept of force on a current carrying conductor in magnetic field? [RRB Group 'D' CBT Exam, 01.09.2022 (Shift-I)]

Loudspeaker, voltmeter, Ammeter, Electric fuse

(1) Loudspeaker
(2) Ammeter
(3) Voltmeter
(4) electric fuse

Correct Answer: (4) electric fuse

Solution:Electric fuse is a safety device used to limit the cur-rent in an electric circuit.

• It melts and breaks the circuit whenever there is an excess flow of current through the circuit.

• It is a low melting point copper or other metal wire that breaks due to heat caused by overvoltage or high load to avoid short circuit or failure to the device.

10. An optical device X has a focal length of -30 cm. X can be: [RRB Group 'D' CBT Exam, 01.09.2022 [Shift-I)]

(1) either concae lens or a convex mirror
(2) either a convex lens or a convex mirror
(3) either a convex lens or a concave mirror
(4) either a concae lens or a concave mirror

Correct Answer: (4) either a concae lens or a concave mirror

Solution:The focal length of a concave mirror is negative and that of a convex mirror is positive.

• This is because in case of concave mirror, the centre of curvature and focus lie in front of the surface of the mirror. Thus, the radius of curvature and focal length are taken as negative.

• According to the sign convention, the focal length of concave lens is always negative.

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