Railway Science (Physics-Electric Current and its Effects) (Part-II)

Total Questions: 50

31. Magnetic lines move from west to east direction and the conductor placed horizontally moves towards the upward direction. In such a case, the direction of induced current is towards: [RRC Group D 13/09/2022 (Afternoon)]

Correct Answer: (c) north
Solution:

Properties of magnetic field lines: They form closed loops and never intersect each other.The magnetic field lines are crowded near the pole where the field is strong and spread apart from each other where the field is weak.They flow from the south pole to the north pole within a magnet and north pole to south pole outside the magnet.

32. When a graph is plotted between V and I : [RRC Group D 14/09/2022 (Morning)]

Correct Answer: (d) an inclined straight line is obtained
Solution:

Ohm's law (1827) states that the current (I) through a conductor between two points is directly proportional to the voltage (V) across the two points. Therefore, R = V/I; where R (resistance) is a constant.

33. If the length of the wire is doubled and cross section area of the wire is halved then the resistivity of the material is: [RRC Group D 14/09/2022 (Afternoon)]

Correct Answer: (d) unchanged
Solution:

(ρ)- The property of a conductor that opposes the flow of electric current through them. It is independent of the shape and size (length and area) of the materials but depends on the nature and temperature of the materials.

34. If the number of turns in a solenoid increases, then: [RRC Group D 14/09/2022 (Afternoon)]

Correct Answer: (a) magnetic field increases
Solution:

A type of electromagnet formed by a helical coil of wire whose length is substantially greater than its diameter, which generates a controlled magnetic field. It works on the principle of electromagnetism. When the electric current passes through the coil, the magnetic field is generated. Factors affecting magnetic field - Strength of the current in the circuit, Density of turns in the coil, the magnetic permeability of the material.

35. On increasing the potential difference applied across a conductor at constant temperature,_______ [RRC Group D 14/09/2022 (Evening)]

Correct Answer: (d) current increases
Solution:

Drift velocity - The average velocity with which free electrons get drifted towards the positive end of a conductor. Vd = 𝐼/𝑛𝐴𝑒 where n - no. of free electrons,  Current flowing, A - Area of cross section, e - Charge on electrons. If we increase the temperature, the resistance will increase resulting in decrease of current and hence drift velocity will decrease.

36. A solenoid carrying constant current can be used as a : [RRC Group D 15/09/2022 (Morning)]

Correct Answer: (b) Source of a constant magnetic field
Solution:

A solenoid is a coil of wire tied across a piston that is made of iron, in the form of a corkscrew. According to the laws of electromagnetism, when an electric current passes via the wire a magnetic field is generated. The magnetic field inside a solenoid is given by B = μₒnI; Therefore, B is directly proportional to I. Where ‘B’ is magnetic field; ‘I’ is current.

37. If three wires of tungsten, manganin and hard rubber are identical in dimension then resistance of ________. [RRC Group D 15/09/2022 (Afternoon)]

Correct Answer: (b) Tungsten is least
Solution:

Resistance, R =  ρ  𝑙/A  (Where ρ - Electrical resistivity of a particular material, l - length, A - area). If ρ increases then R also increases. Electrical resistivity (ρ) of some elements: Tungsten (5.20 × 10⁻⁸), Manganin (44 × 10⁻⁶), Hard rubber (10¹³ to 10¹⁶), Ebonite (10¹⁵ to 10¹⁷), Silver (1.60 × 10⁻⁸ - lowest among all element), Copper (1.62 × 10⁻⁸), Aluminum (2.63 × 10⁻⁸).

38. When magnetic lines of forces are more crowded in the region of magnetic field, this indicates the presence of: [RRC Group D 16/09/2022 (Morning)]

Correct Answer: (c) strong magnetic field
Solution:

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. Properties - They form closed loops, They never intersect with each other, The magnetic field lines are crowded near the pole where the field is strong and spread apart from each other where the field is weak.

39. Straight conductor carrying current is kept along the axis of a closed circular loop of a conductor. If we change the direction of the current continuously in the straight conductor: [RRC Group D 16/09/2022 (Afternoon)]

Correct Answer: (b) induced current in the loop is not constant
Solution:

In every state of electromagnetic induction, the direction of the induced current is such that it opposes the cause that has produced it. This law is consistent with the law of conservation of energy.

40. The magnitude of force that acts on the arms of an armature is the maximum when the length of the arms are: [RRC Group D 17/09/2022 (Morning)]

Correct Answer: (b) perpendicular to the magnetic field
Solution:

An electric motor is a rotating device that converts electrical energy to mechanical energy. Working principle - An electric motor (dc motor) works on the principle that when an electric current is passed through a conductor placed normally in a magnetic field, a force acts on the conductor as a result of which the conductor begins to move and mechanical energy is obtained.