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

Total Questions: 50

21. If two parallel straight conductors are carrying current in the same direction, then the directions of the magnetic fields produced will be: [RRC Group D 30/09/2022 (Afternoon)]

Correct Answer: (b) opposite to each other
Solution:

Two current carrying conductors attract each other when the current is in the same direction and repel each other when the current is in the opposite direction. This can be verified using Fleming's left-hand rule - The thumb points towards the direction of the force experienced by the conductor, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the electric current.

22. The symbol for resistance (R) is denoted with _____. [RRC Group D 06/10/2022 (Morning)]

Correct Answer: (c)
Solution:

23. The compass needle gets deflected when it is brought near to a bar magnet because it _____________. [RRC Group D 06/10/2022 (Afternoon)]

Correct Answer: (b) is a tiny magnet
Solution:

The Compass needle is a small magnet. That is why, when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected near the magnet bar.

24. Which of the following represents material in the increasing order of their resistance? [RRC Group D 06/10/2022 (Evening)]

Correct Answer: (d) Conductors, alloys, insulators
Solution:

Resistance: The opposition that a substance offers to the flow of electric current. Insulators: glass, air, wood, plastic and rubber. Alloys: Steel, Nichrome, Bronze, Brass, Duralumin, Solder. Conductors: Copper, Brass, Steel, Gold, Aluminium. Resistivity: Electrical resistance of a conductor of unit cross-sectional area and unit length; It is same for a given material i.e. different for different materials; Highest for insulators and lowest for conductors.

25. In an electric motor, the forces acting on the arms of the armature of the motor that are perpendicular to the direction of magnetic field are: [RRC Group D 07/10/2022 (Morning)]

Correct Answer: (c) equal in magnitude and opposite in direction
Solution:

It states that if we arrange our thumb, forefinger and middle finger of the left-hand perpendicular to each other, then the thumb points towards the direction of the force experienced by the conductor, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the electric current.

26. The presence of a magnetic field can be determined by _________. [RRC Group D 07/10/2022 (Morning)]

Correct Answer: (c) a magnetic needle
Solution:

A slender bar of magnetized steel usually suspended on a low friction mounting and used in a magnetic compass to indicate the direction of the earth's magnetic poles. Galvanometer - Instrument for measuring a small electrical current or a function of the current by deflection of a moving coil. Voltmeter - Instrument used for measuring electric potential difference between two points in an electric circuit. Ammeter - An instrument for measuring the current flowing in a branch of a circuit.

27. Which of the following is/are the correct conclusion(s) from Oersted's experiment? [RRC Group D 07/10/2022 (Afternoon)]

(a) A magnetic compass needle placed along the side of a current carrying conductor deflects
(b) A current carrying conductor will produce a magnetic field around it.
(c) The direction of deflection of the compass needle placed along the side of a current carrying conductor does not change with reversal in the direction of current.

Correct Answer: (a) Only (a) and (b) are correct
Solution:

Oersted's experiment (1820)- It shows the relationship between electricity and magnetism. In his experiment he noticed that when a magnetic compass is placed near a current carrying wire, it produces a magnetic field around it which deflects the compass needle.

28. The circumference of magnetic field lines___________as we move away from a current carrying a straight conductor. [RRC Group D 07/10/2022 (Afternoon)]

Correct Answer: (b) increases
Solution:

The magnetic field produced by a current-carrying conductor is inversely proportional to the distance of the point from the conductor. Thus, as we move away from a current-carrying conductor, the intensity of the magnetic field decreases so the circumference between the magnetic field lines Increases. Magnetic Field is the region around a magnetic material or a moving electric charge within which the force of magnetism acts. SI Unit - Tesla, Symbol - B or H, Base Unit - (Newton.Second)/Coulomb.

29. An example of a series circuit is _____________. [RRC Group D 07/10/2022 (Evening)]

Correct Answer: (a) decoration lights
Solution:

Series circuit - All components are connected end-to-end to form a single path for current flow. Examples - Water heater, Freezers, Refrigerators, Lamps, Well water pump, Flashlights. Parallel circuit -The circuit in which all the components are connected in parallel can be called a parallel circuit, the same voltage is available across each component. Examples - car headlights, the wiring system at home, Street lights, DC Filter Circuit, Fire Alarm Circuit .

30. The induced emf developed in a conductor when it is moved in a direction parallel to the magnetic field is [RRC Group D 07/10/2022 (Evening)]

Correct Answer: (b) Zero
Solution:

The magnetic field linked with the conductor does not change when it moves parallel to the magnetic field. Hence, emf is not induced. According to Faraday's law of  electromagnetic induction ⇒ e  = - N 𝑑Φ/𝑑t,
Φ = BA cosθ, then e = - N 𝑑 (𝐵𝐴 𝑐𝑜𝑠θ)/𝑑t , Where N = number of turns, e = induced e.m.f and B is the magnetic field strength over an area A, at an angle θ. When magnetic field lines are parallel to the conductor then the angle between them is 0°. If we put θ = 0° then cos 0° = 0, Hence e = 0.