Electric current – part (1)

1. Current density is : [69th B.P.S.C (pre) 2023]

(a) a scalar quantity
(b) a vector
(c) dimensionless
(d) none of the above

Correct Answer: (b) a vector

Solution:The amount of current travelling per unit cross-section area of conductor is called as current density and expressed in amperes per square meter .it is a vector quantity. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in the space ,its direction being that of the motion of the positive charges at this point.

2. A 100 watt electric bulb is used for 10 hours. What will be the cost of electricity consumed, if the consumption cost is Rs. 5 per unit ? [R.A.S./R.T.S (PRE) 2012]

(a) Rs. 5
(b) Rs. 10
(c) Rs. 25
(d) Rs. 50

Correct Answer: (a) Rs. 5

Solution:Energy consumption of 100 watt electric bulb which is used for 10 hour =100×10
=1000 watt hour
=1 kilowatt hour
= 1 unit
according to question the cost of 1 unit of electricity =Rs. 5.

3. If a bulb of 100 watt burns for 10 hours the expenditure of electricity will be - [41st B.P.S.C. (Pre) 1996]

(a) 0-1 unit
(b) 1 unit
(c) 10 unit
(d) 100 unit

Correct Answer: (b) 1 unit

Solution:Energy consumption of 100 watt electric bulb which is used for 10 hour =100×10
=1000 watt hour
=1 kilowatt hour
= 1 unit
according to question the expenditure of electricity will be= 1 unit

4. 15 bulbs of 100 watt burns for 10 hour the expenditure of electricity will be - [U.P.R.O/A.R.O (pre) 2023]

(a) 71 units
(b) 15 units
(c) 73 units
(d) none of the above

Correct Answer: (b) 15 units

Solution:Solution:

Total wattage: 15 bulbs ×100 watts/bulb = 1500 watts
Total kilowattage: 1500 watts / 1000 = 1.5 kilowatts (kW)
Total kilowatt-hours (kWh): 1.5 kW × 10 hours = 15 kWh
Units of electricity: 1 kWh = 1 unit of electricity.
Therefore, 15 kWh = 15 units.

Therefore, The correct answer is 15 units.

5. Five bulbs each of 100 watt capacity in a tunnel are illuminated continuously for twenty hours the consumption of electricity will be : [U.P.P.C.S.(pre) 2017]

(a) one units
(b) two units
(c) ten units
(d) twenty units

Correct Answer: (c) ten units

Solution:Consumption of electricity by one bulb
(no. of unit)=watt×hour/1000
=100×20/1000
=2 units
thus consumption of electricity by 5 bulbs = 2×5
=10 units

6. The value of 1 kilowatt hour is - [U.P.P.C.S.(pre) 2006]

(a) 3.6×10⁶J
(b) 3.6×10 ³J
(c) 10³ J
(d) 10⁵ J

Correct Answer: (a) 3.6×10⁶J

Solution:1 kilowatt hour =1 (killowatt) (hour)

= (1000 joule /sec) (3600 sec)

=3.6×10⁶ J

thus the option (a) is correct

7. An electric bulb of 100 watt is used for 4 hour the unit of electric energy used is - [U.P. Lower Sub (pre) 2009]

(a) 400
(b) 25
(c) 4
(d) 0.4

Correct Answer: (d) 0.4

Solution:The electric energy consumed
= 100 watt ×4 hour
=400 watt hour
=400/1000 kilowatt hour
=0.4 kilowatt hour
=0.4 unit

8. Electricity consumption bill is based on the measurement of - [40th B.P.S.C(Pre) 1995]

1.watt
2.voltage
3.ohm
4.ampere
select your answer of the following codes:

(a) only 1
(b) 1 and 2
(c) 2 and 3
(d) 1 and 4

Correct Answer: (a) only 1

Solution:Electricity consumption bill is based on the measurement of kilowatt hour the kilowatt hour is the unit of electricity consumption equal to 1000 watt in 1 hour (1 unit ).

Since watt is related to power, which is used to calculate the electricity consumption, the most relevant answer from the given choices is the watt.

Therefore, the most accurate answer from the provided options is 1. watt. However, it is important to understand that the bill is based on kilowatt hours.

9. How many units of electricity will be consumed if you use a 60-watt electric bulb for 5 hours everyday for 30 days ? [R.A.S/R.T.S (PRE) 2003]

(a) 12
(b) 9
(c) 6
(d) 3

Correct Answer: (b) 9

Solution:We know that
number of unit =watt×hour /1000
=60×30×5/1000=9 unit

10. An electric bulb is connected to 220 v generated the current is 0.5 A. The power of the bulb is: [Chhattisgarh P.C.S.(PRE) 2016]

Correct Answer: (a) 110 w

Solution:Given
v=220 v
i=0.5 A
we know that
p=w/t=vit/t (∴ w=vit )

⇒vi=220×0.5=110 watt

Electric current – part (1)