Railway Science (Physics-Electric Current and its Effects)

Total Questions: 50

1. The filament of a bulb is made extremely thin and long in order to achieve: [RRC Group D 17/08/2022 (Morning)]

Correct Answer: (a) High resistance
Solution:

High resistance. Tungsten is used in filament of the bulb because it has the highest melting point of any metal and the higher the temperature, the higher the efficiency and the whiter the light. Gases in the bulb – helium, neon, nitrogen and argon.

2. Which of the following statements is/are correct for a current carrying solenoid? [RRC Group D 17/08/2022 (Morning)]

(i) It can be used to magnetize a piece of soft iron.
(ii) It acts like a bar magnet
(iii)The field lines are concentric circles

Correct Answer: (d) Both (i) and (ii)
Solution:

Both (i) and (ii). The solenoid is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. Magnetic field due to a straight current-carrying conductor - When current is passed through it, a magnetic field is produced around it. Magnetic field due to current through a circular loop - Every point on the wire carrying current gives rise to a magnetic field that appears as straight lines at the center.

3. The I-V graph of three resistances R₁ , R₂ and R₃, is shown in the figure below. The correct relation between R₁ R₂ and 𝑅₃ is: [RRC Group D 17/08/2022 (Afternoon)]

Correct Answer: (b) R₃ < R₁ < R₂
Solution:

R₃ < R₁ < R₂ Since the increase in Current (I) is most in 𝑅₃ , the
value of 𝑅₃ will be least because Current is inversely proportional to the
Resistance(R). I ∝ 1/R , I = V/R.

4. Which of the following rules is used to determine the direction of induced current due to the motion of coil at right angle to the magnetic field? [RRC Group D 17/08/2022 (Evening)]

Correct Answer: (a) Fleming's right-hand rule
Solution:

Fleming's right-hand rule. Fleming’s left-hand rule - When a current-carrying conductor is placed in an external magnetic field, the conductor experiences a force perpendicular to both the field and the current flow’s direction. Right-Hand Thumb Rule (Maxwell's corkscrew rule) - If a current-carrying conductor is imagined to be held in your right hand such that the thumb points along the direction of the current, then the direction of the wrapped fingers will give the direction of magnetic field lines.

5. Which of the following situations is/are possible? [RRC Group D 17/08/2022 (Evening)]

(A) Magnetic field lines can be parallel to each other.
(B) Magnetic field lines can be concentric circles.
(C) Magnetic field lines can intersect each other.

Correct Answer: (a) Both (A) and (B)
Solution:

Both (A) and (B). Magnetic field lines: They never cross each other. The density of the field lines indicates the strength of the field. They always make closed loops.They always emerge or start from the north pole and terminate at the south pole. In a uniform magnetic field, the field lines are parallel and equidistant straight lines.

6. Which of the following statements is/are correct? [RRC Group D 18/08/2022 (Morning)]

(i) Magnetic field strength is strongest at the center of a bar magnet.
(ii) No two magnetic field lines can intersect.
(iii) Magnetic field lines always form closed continuous curves.

Correct Answer: (a) Both (ii) and (iii)
Solution:

Both (ii) and (iii). Magnetic field - Discovered by Hans Christian Oersted in 1820. Properties of Magnetic Field Lines - The density of the field lines indicates the strength of the field, always emerging from the north pole and terminating at the south pole, The magnetic field is strongest at the poles as the field lines are very close to each other near the poles. Types of Magnetic Substances - Diamagnetic substances, Paramagnetic substances, and Ferromagnetic substances.

7. An AC generator works on the principle of: [RRC Group D 18/08/2022 (Morning)]

Correct Answer: (a) electromagnetic induction
Solution:

states that electromotive force (EMF or voltage) is generated in a current-carrying conductor that cuts a uniform magnetic field. AC generators (Founded by Charles F. Brush in the 1860s). Heating effect of Electric Current - When an electric current is passed through a conductor, it generates heat due to the hindrance caused by the conductor to the flowing current. Electromagnetism (William Sturgeon) - Deals with the electromagnetic force that occurs between electrically charged particles.

8. A metallic wire having resistivity ρ is cut into four equal parts. The resistivity of each part is: [RRC Group D 18/08/2022 (Afternoon)]

Correct Answer: (c) ρ
Solution:

Resistance offered by an object per unit length and per unit cross sectional area at a specified temperature. As resistivity depends upon the material of the wire and temperature. If we cut the wire into 4 equal parts then the length of the wire will be changed but the resistivity of the wire will remain the same i.e.(⍴). SI unit of Resistivity is ohm m.

9. To connect a number of resistors in parallel can be considered equivalent to: [RRC Group D 18/08/2022 (Afternoon)]

Correct Answer: (d) increasing cross sectional area of the conductor
Solution:Resistance of a conductor,
R = ρ l/A.
Resistance is inversely proportional to the area of the cross - section of the conductor i.e., the more the area of the cross-section of the conductor, the less is the resistance. In a parallel combination of resistors,
1/R = 1/r₁ + 1/r₂
Hence, the effective resistance in a parallel combination of resistors decreases.

10. The magnetic field produced due to a circular coil carrying a current having six turns will be how many times that of the field produced due to a single circular loop carrying the same current? [RRC Group D 18/08/2022 (Afternoon)]

Correct Answer: (d) 6 times
Solution:

The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it. Therefore, if there is a circular coil having 6 turns, the field produced is 6 times as large as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.