Physics (Part-IX) (Railway)

Total Questions: 50

11. The appearance of a stick at the Interface when immersed in water is an example of_________. [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1) transmission of light
(2) displacement of light
(3) refraction of light
(4) reflection of light

Correct Answer: (3) refraction of light

Solution:When a stick is dipped in water in a container, rays of light from the tip of the stick bend away from the normal as they go from water to air.

• It because of the refraction of light.

12. A concave lens of focal length 30 cm forms an image of an object placed at 60 cm from it. The position and nature of the image formed will be: [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1)-20cm, real and inverted
(2) 20 cm, real and Inverted
(3) -20cm, virtual and erect
(4) 20cm, virtual and erect

Correct Answer: (3) -20cm, virtual and erect

Solution:The relation between object distance, image distance and focal length of a concave lens is given by the formula 1 / v - 1 / u = 1/f or 1/v = 1/f+ 1/u, where v distance of image from lens, u = distance of object from lens and f = focal length of lens

• So, according to the question l / v = 1/30 + 1/60 = 3/60

• ∴ v = - 20 cm

• A concave lens always forms a virtual, erect, and diminished image between the F and 2F of the lens.

13. Which of the following is used to study the direction of rotation of a coil in a magnetic field in an electric motor? [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1) Left hand thumb rule
(2) Fleming's right hand rule
(3) Right hand thumb rule
(4) Fleming's left hand rule

Correct Answer: (4) Fleming's left hand rule

Solution:According to Faraday's law of electromagnetic induction, when a conductor moves through a magnetic field, an electric current is induced in it.

• Fleming's left-hand rule is used to find the direction of the force acting on the current carrying conductor placed in a magnetic field.

• It is used in electric motors.

14. In an electric motor, the direction of flow of current is reversed using: [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1) a carbon brush
(2) a split ring
(3) a motor brush
(4) armature winding

Correct Answer: (2) a split ring

Solution:The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coll after every half rotation of the coil.

• Due to this, the coil continues to rotate in the same direction.

• It is also known as a commutator.

15. A coin of diameter 10cm is placed at a distance 3.5f from the pole of a concave mirror of focal length f. The linear magnification and the diameter of the image are. [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1) 3/5 and 5cm, respectively
(2) 4/5 and 8cm, respectively
(3) 1/5 and 2cm, respectively
(4) 2/5 and 4cm, respectively

Correct Answer: (4) 2/5 and 4cm, respectively

Solution:Total distance = f

U = 7/2 f , V = ?

1/f = 1/u = 1/v

⇒ 1/f = 2/7 f * 1/v

⇒ 1/v = 7-2/7 f * 5/7 f

⇒ V = 7 f / 5

Magnificotion = 7/5 f/7 /2 f = 2/5

Now,

m = 1/10

⇒ 2/5 = 1/10

⇒ 1 = 20/5 4 cm

16. The heat generated H due to Joule's heating effect is directly proportional to__________. [RRB Group 'D' CBT Exam, 27.09.2022 (Shift-I)]

(1) cube of the current
(2) square of the current
(3) square root of the current
(4) cube root of the current

Correct Answer: (2) square of the current

Solution:H = I² Rt.

so, heat produced is directly proportional to the square of electric current produced.

17. When white light is incident on a prism, it undergoes dispersion. In this context, identify the correct option. [RRB Group 'D' CBT Exam, 28.09.2022 (Shift-II)]

(a) Red colour light bends most in the prism.

(b) Speed of violet colour light is the slowest in the prism.

(d) Violet is the top most colour and red is the bottom most colour when the prism is erect.

(e) Dispersion is also the reason for the formation of rainbow.

(1) (b), (d) and (e)
(2) (b), (c) and (d)
(3) (a), (c) and (d)
(4) (b), (c) and (e)

Correct Answer: (4) (b), (c) and (e)

Solution:The light that bends the least is red colour and the light that bends the maximum is violet colour light.

• Violet colour refracts the most because violet light in the visible light spectrum has a smaller wavelength of about 400 nanometers when compared to red at 650 nanometers.

• During dispersion of white light by a prism, different colors travel with different speed hence they split in prism.

• Red travels the faster while violet travels slowest so Red is on top and violet is at bottom.

18. Which of the following rules or laws correctly describe the direction of force, magnetic field and current at the same instant? [RRB Group 'D' CBT Exam, 28.09.2022 (Shift-II)]

(1) Ampere's circuital law
(2) Right hand thumb rule
(3) Fleming's left hand rule
(4) Palm rule

Correct Answer: (3) Fleming's left hand rule

Solution:Fleming's left-hand rule When a current-carrying conductor is kept in a magnetic field, a force applies on it; the direction of this force can be determined using Fleming's Left-Hand Rule.

• Similarly, if a moving conductor is placed in a magnetic field, an electric current will be induced in it. The direction of the induced current can be determined using Fleming's Right-Hand Rule.

• So, Fleming's left-hand rule describes the direction of force, magnetic field and current at the same instant.

19. A concave mirror of focal length f produces a real image at a distance from the pole, when an object is kept at the distance u from the pole. Here, focal length of the given mirror is: [RRB Group 'D' CBT Exam, 28.09.2022 (Shift-II)]

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

Correct Answer: (3) (uv)/(v+v)

Solution:The equation relating the object distance (u), the image distance (v) and lens focal length (f) is called mirror formula.

• 1/f, where u is the Object distance, v is the Image distance, and f is the Focal Length

• It can also be expressed as 1/f = u + v/vu

• ∴ f=uv/u + v

20. Which of the following statements with regard to the principal axis of a spherical mirror is are correct? [RRB Group 'D' CBT Exam, 28.09.2022 (Shift-II)]

(a) The pole on the principal. axis is similar to the origin of a cartesian coordinate axes plane.

(b) Distances measured from the pole, along the principal axis opposite to the direction of incident light are negative.

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

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

Solution:Sign convention is a set of rules to set signs for image distance, object distance, focal length, etc for mathematical analysis of image formation. According to it:

• Height of an object is always considered positive.

• If an image is formed above the principal axis, its height is taken as positive and if below the principal axis then it is taken as negative.

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