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Electricity (Part-2)

📆 December 7, 2024

Total Questions: 54

31. The frequency of direct current is _______ . [S.S.C. Online Graduation Level (T-1) 3.09.2016 (Shift-III)]

Correct Answer: (a) Zero
Solution:

The frequency of direct current (DC) is zero (0 Hz).

  • Definition of Frequency:
    Frequency refers to the number of complete cycles of a waveform that occur in one second. It describes how often the direction of the current changes.
  • Direct Current Characteristics:
    Direct current flows in only one direction. The polarity (positive and negative ends) remains constant over time.
  • No Change in Direction:
     Since the direction of the current in DC never reverses, there are no cycles or oscillations. Therefore, the rate of change in direction is zero.

Think of it like a steady stream of water flowing in one direction – there are no waves or changes in flow direction, so the "frequency" of changes is zero.

32. Find the resistance (in mega Ω) of a wire of length 10 m, cross-sectional area 1 cm² and made of a material of resistivity 100 Ωm. [S.SC. Online CHSL (T-1) 22.03.2018 (Shift-I)]

Correct Answer: (d) 10
Solution:Since the length of the wire L = 10 m and its cross-sectional area is A = 1 cm² = 1 × 10⁻⁴ m²
and resistivity of the wire 100 Ωm.
∴ R = ρ ( L/A ) (Form the formula)
R = 100 m² × 10/1 × 10⁻⁴ m²  = 100 × 10 ×10⁷Ω
= 10⁶ × 10Ω ⇒ 10 mega ohm.

33. The amount of heat produced by passing an electric current in a wire does not depend on_______ . [S.S.C. Online MTS (T-1) 17.09.2017 (Shift-III)]

Correct Answer: (d) None of these
Solution:The value of heat produced due to a current flowing in a conducting wire is expressed by the formula H = I² Rt.
That is, the heat generated H ∝ R here R is the resistance of the wire. Now the value of R also depends on the material, length and thickness of the wire. Hence heat H will also depend on these quantities.
So the correct answer will be indicated by option (d).

34. The inverse of resistance is conductivity. If the unit of resistance is ohm, then the unit of conductivity will be_______ . [S.S.C. Online MTS (T-I) 16.09.2017 (Shift-I)]

Correct Answer: (a) Ohm⁻¹
Solution:The inverse of resistance is conductivity.

G = 1/R [where G is conductance]

We know that the unit of resistance is ohm. Hence the unit of conductivity will be ohm⁻¹.

35. Weber is the unit of? [S.S.C. Online Constable GD 3.03.2019 (Shift-I)]

Correct Answer: (b) Magnetic flux
Solution:In physics, Weber is the unit of magnetic flux. The unit of capacitance is Farad. The unit of electrical conductivity is siemens/meter. The unit of magnetic flux density is tesla.

36. The SI unit of magnetic flux is known as: [S.S.C. JE Civil Exam 30.10.2020 (Shift-1)]

Correct Answer: (c) Weber
Solution:One Weber is defined as the magnetic flux that, linking a circuit of one turn, produces in it an electromotive force of one volt if it is reduced to zero at a uniform rate in one second (based on Faraday's law of induction).
  • 1 Weber = 1 Volt-second (V⋅s)
  • 1 Weber = 1 Tesla-square meter (T⋅m²) (where Tesla is the unit of magnetic flux density)
  • 1 Weber =  Maxwells (Mx) (the CGS unit of magnetic flux)

37. What is the unit of the physical quantity, magnetic flux density? [S.S.C. Online CHSL (T-1) 25.01.2017 (Shift-I)]

Correct Answer: (d) Tesla
Solution:

The Tesla (T) is the SI derived unit of magnetic flux density (also known as magnetic B-field strength or magnetic induction). 

What it measures:
Tesla quantifies the strength of a magnetic field. It represents the amount of magnetic flux per unit area. Imagine the number of magnetic field lines passing through a specific area; Tesla measures the density of these lines.

38. Flemings "Left Hand Rule" is associated with the effect of- [S.S.C. Online Graduation Level (T-I) 6.09.2016 (Shift-III)]

Correct Answer: (d) Magnetic Field on current
Solution:According to Fleming's left-hand rule, if we keep the forefinger, middle finger, and thumb of our left hand at right angles to each other, then the index finger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb indicates the direction of the force acting on the conductor.
OMTEX CLASSES: Fleming's left hand rule.

39. Which finger shows the direction of current in Fleming's left hand rule? [S.S.C. Online MTS (T-1) 8.08.2019 (Shift-I)]

Correct Answer: (c) Middle finger
Solution:According to Fleming's left-hand rule, if we keep the forefinger, middle finger, and thumb of our left hand at right angles to each other, then the index finger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb indicates the direction of the force acting on the conductor.
OMTEX CLASSES: Fleming's left hand rule.

40. _______through a plane surface is the product of the magnetic flux density normal to the surface and the area of the surface. [S.S.C. Online CHSL (T-1) 19.01.2017 (Shift-III)]

Correct Answer: (c) Magnetic flux
Solution:Magnetic flux () is a measure of the total magnetic field that passes through a given area. It's a scalar quantity, meaning it has magnitude but no direction.
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