Basic Electrical Mcqs

If 1 A current flows in a circuit, the number of electrons flowing through this circuit is

A. 0.625 × 1019
B. 1.6 × 1019
C. 1.6 × 10-19
D. 0.625 × 10-19

The charge of one electron is 1.6 × 10 – 19 coulomb. Again 1 A current means transferring of 1 coulomb charge per one second.

The resistivity of the conductor depends on

A. area of the conductor.
B. length of the conductor.
C. type of material.
D. none of these.

The resistivity is a property of material, defined as the resistance between two opposite faces of a cube of a material of unit volume. That is why resistivity is only the unique property of material and it does not depend upon the dimension of any piece of material.

The resistance of a conductor of diameter d and length l is R Ω. If the diameter of the conductor is halved and its length is doubled, the resistance will be

A. R Ω
B. 2R Ω
C. 4R Ω
D. 8R Ω

As per law of resistance, the resistance of the conductor is inversely proportional to its cross-sectional area i.e. it is inversely proportional to the square of the diameter of cross-sectional area of the conductor. As per same law of resistance, the resistance of the conductor is directly proportional to the length of the conductor.

How many coulombs of charge flow through a circuit carrying a current of 10 A in 1 minute?

A. 10
B. 60
C. 600
D. 1200

1 Ampere current means flowing of 1 Coulomb charge per second. That means 10 A current in 1 minute or 60 seconds implies 10 × 60 = 600 coulombs.

The unit of resistivity is

A. Ω.
B. Ω – metre.
C. Ω / metre.
D. Ω / m².

Instantaneous power in inductor is proportional to the

A. product of the instantaneous current and rate of change of current.
B. square of instantaneous current.
C. square of the rate of change of current.
D Temperature of the inductor.

The instantaneous voltage across the inductor is expressed as the product of inductance and rate of change of current through it. Power is expressed as the product of current and voltage. Hence instantaneous power in an inductor is proportional to the product of instantaneous current and rate of change of current through it.

The voltage induced in an inductor is represented as,

A. product of its inductance and current through it.
B. ratio of its inductance to the current through it.
C. ratio of the current through it to its inductance.
D. product of its inductance and rate of change of current through it.

The instantaneous voltage across the inductor is expressed as the product of inductance and a rate of change of current through it as it doesn’t allow any certain change of current through it. Voltage induced in an inductor is written as

Magnetic flux has the unit of

A. Newton
B. Ampere-turn
C. Weber
D. Tesla

The unit of magnetic flux is called Weber in honor of famous scientist Wilhelm Eduard Weber (1804 – 1891). Magnetic flux has also another unit named Maxwell. 1 Maxwell = 10-8 Weber.

 If P is the power of a star connected system then what will be power of an equivalent delta connected system?A. P
B. 3P
C. P/3
D. None of the above

Assume 3 numbers of pure resistive loads each of value R.
When these loads are connected in delta the power in each resistor is V^2/R and the total power is 3×V^2/R.
When these loads are connected in star the voltage applied across each = V/(sqrt of 3). Power in each load becomes = V^2/(3×R) . and the total load is =(3×V^2)/(3×R)=V^2/R. You can see this is 3 times less than the total power when the loads are connected in delta.
One important point is that the loads should withstand higher voltage (line voltage) and higher current when connected in delta than when they are connected in star
so power in delta is 3 time power correct answer is 3P

 

Which of the followings is/are active element?

A. Voltage source
B. Current source
C. Both
D. None of these.

Active elements are capable of delivering energy independently for long time or ideally infinite time. Both voltage and current source are active element and they can change energy level of a circuit.