Electric current - part (1)

Electric current – part (1)

Total Questions: 50

31. Assertion (A) : light emitting diode lamps offer longer service life as compared to compact flourescent lamps (CFL): [R.A.S/R.T.S (PRE) 2013]

Reason (R) : light emitting diodes lamps are the more energy efficient as compared to the compact flourescent lamps (CFL).
select the correct answer using the codes given in the below

(a) both (A) and (R) are correct and (R) is the correct explanation of (A).
(b) both (A) and (R) are correct and (R) is not the correct explanation of (A).
(c) (A) is the correct but (R) is wrong.
(d) (A) is the wrong but (R) is correct.

Correct Answer: (a) both (A) and (R) are correct and (R) is the correct explanation of (A).

Solution:In light emitting diode lamps gallium arsenide is used as main light emission component, which converts electric into light. its life span is greater than that of the CFL because of LED lamps consumes less energy than the CFL.

32. Total resistance of the circuit having two parallel resistor is 1.403 kilo - ohm if the one of the resistor is 2.0 kilo-ohm then the other resistor will be: [66th B.P.S.C. (PRE) 2020]

(a) 1.403 kilo-ohm
(b) 2.0 kilo-ohm
(c) 3.403 kilo-ohm
(d) 4.70 kilo-ohm
(e) none of the above /more than one of the above.

Correct Answer: (d) 4.70 kilo-ohm

Solution:If the total resistance of a parallel circuit is R then
1/R=1/R₁+1/R₂ +.............................................
according to the question
⇒1/1.403=1/2+1/R₂
⇒1/R₂ =1/1.403-1/2
⇒1/R₂ =(2-1.403)/2.806
⇒R₂ =2.806/0.597=4.70 kilo-ohm.

33. Of the two bulbs in the house one glow brighter than the other in this context which of the following statement is correct ? [U.P. Lower Sub (pre) 2008, U.P.P.C.S.(pre) 2009]

(a) the brightness does not depend on the resistance.
(b) both the bulb have same the resistance.
(c) the bright bulb has high resistance.
(d) the dim bulb has larger resistance.

Correct Answer: (d) the dim bulb has larger resistance.

Solution:The bulb which decays more energy will generate more brightness.
power=voltage(V)×current(I)
it is known that V=I×Resistance (R)
P=V² /R

P∝1/R thus the bulb of high resistance decays the low energy and will generate dim light.

34. How two identical bulbs should be connected to get maximum light? [U.P.R.O/A.R.O. (Pre) 2021]

Case1 : Both bulb connected in series.

Case2: Both bulb connected in parallel.

(a) In case 1 more
(b) In case 2 more
(c) Same in both 1 and 2
(d) Nothing can be said

Correct Answer: (b) In case 2 more

Solution:Bulbs in parallel are brighter than bulbs in series. In a parallel circuit the voltage for each bulb is the same, while the parallel combination of resistors reduces the effective resistance of the circuit. The power dissipated by a bulb is given by
P = (V² ) / R
where V is the voltage of the light bulb and R is the electrical resistance.
The total resistance of the series circuit is
R_Series= R+R=2R.
The total resistance of the parallel circuit is
1/R_parallel=1/R+1/R
Or
R_parallel=R/2
therefore the power for the light bulbs in series is
P_Series =V²/2R
and the power for the light bulbs in series is
P_parallel =2V²/R
hence from the above question it is clear that in parallel circuit the bulb will shine brightly.

35. A voltage of 15 volt is applied across a colour coded carbon resistor with first, second and third rings of brown, green and black colours. What is the current flowing through the resistor ? [U.P. R.O/A.R.O. (Pre) 2023]

(a) 1 ampere
(b) 2 ampere
(c) 3 ampere
(d) None of the above.

Correct Answer: (a) 1 ampere

Solution:Resistor code value for brown colour = 1 (A)
Resistor code value for green colour = 5 (B)
Resistor code value for black colour = 0 (C)
We know that first two bands (rings) indicate the first two
significant digits of resistance value and the third band serves as a multiplier.
So, Resistance value of resistor
= (A ×10 + B) × 10^c
= (1 ×10 + 5) × 10⁰
= 15 ×1 = 15 Ohm (Ω)
Current (i) = Voltage(V)/ Resistance(R)

=15/15=1 ampere

Hence, the current flowing through the resistor is 1 ampere.

36. A dynamo which is said to generate electricity actually acts as a: [U.P.P.C.S. (Mains) 2009]

(a) Source of ions.
(b) Source of electric charge.
(c) Converter of energy.
(d) Source of electrons.

Correct Answer: (c) Converter of energy.

Solution:A dynamo, which is also known as an electrical generator produces direct current through a commutator. It is basically a device which converts mechanical rotation into electric current according to Faraday's law.

37. 'Dynamo' is a device, which converts: [U.P. P.C.S. (Pre) 2016 39 B.P.S.C. (Pre) 1994 U.P.P.C.S. (Pre) 1993 U.P.P.C.S. (Pre) 1992]

(a) Chemical energy into electrical energy.
(b) Electrical energy into mechanical energy.
(c) Mechanical energy into electrical energy.
(d) Electrical energy into chemical energy.

Correct Answer: (c) Mechanical energy into electrical energy.

Solution:A dynamo is an electrical generator that produces direct current with the use of a commutator. It converts mechanical energy into electrical energy.

38. Dynamo is a machine which is used for: [U.P.P.C.S. (Mains) 2012 R.A.S/R.T.S.(Pre) 2012]

(a) Conversion of high voltage to low.
(b) Conversion of electrical energy to mechanical.
(c) Conversion of mechanical energy to electrical energy.
(d) Conversion of low voltage to high voltage.

Correct Answer: (c) Conversion of mechanical energy to electrical energy.

Solution:A dynamo is an electrical generator that produces direct current with the use of a commutator. It converts mechanical energy into electrical energy.

39. Turbines and Dynamos are used to convert which energy to electrical energy? [44th B.P.S.C. (PRE) 2000]

(a) Chemical energy.
(b) Solar energy.
(c) Mechanical energy.
(d) Magnetic energy.

Correct Answer: (c) Mechanical energy.

Solution:A dynamo is an electrical generator that produces direct current with the use of a commutator. It converts mechanical energy into electrical energy.

40. When electrical energy is converted into motion in ideal condition: [47th B.P.S.C. (Pre) 2005]

(a) There is no heat loss
(b) Heat loss is 50 percent
(c) Heat loss is 30 percent
(d) Heat loss is 80 percent

Correct Answer: (a) There is no heat loss

Solution:When electrical energy is converted into motion in ideal condition, there is no heat loss.

« Previous 1 2 345 Next »

Electric current – part (1)