Tag: electric current and its effects

Questions Related to electric current and its effects

An electric bulb of $30\ W$ consumes $0.72$ units of energy in a day. Find the number of hours it is working in a day?

physics electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $6\ hrs$

  2. $12\ hrs$

  3. $18\ hrs$

  4. $24\ hrs$

Show answer
Correct Option: D
Explanation:
Given :   $P =0.030$ kW
Energy consumed per day       $E= 0.72\ \text{units}$$ = 0.72\ kWh$
Using   $E = P\times t$
$\therefore$   $0.72 = 0.03\times t$               
$\implies t = 24\ hrs$

For a heater rated at 4.4 kW; 220 V  . Calculate  the energy consumed by the heater in 4 hours? 

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. 12 kWh

  2. 17.6 kWh

  3. 0 kWh

  4. 4.4 kWh

Show answer
Correct Option: B
Explanation:

Given :   $P = 4.4$ kW             $t = 4$ h

$\therefore$ Energy consumed in 4 h       $E= Pt =4.4\times 4 = 17.6$ kWh

How much units of energy is consumed in operating ten 50 watt bulbs for 10 hours per day in a month (30 days)

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. 100 kwh

  2. 150 kwh

  3. 160 kwh

  4. 500 kwh

Show answer
Correct Option: B
Explanation:
Given :    $P = 0.05$ kW               $t = 10$ hours per day 
Number of bulbs     $n = 10$
Energy consumed per day       $E= nPt = 10 \times 0.05\times 10 = 5$ kwh  per day
Total energy consumed in 30 days    $E _t = 5\times 30 = 150$ kWh

Which of the following is true for electrical energy?

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $E = P \times t$

  2. $E = \dfrac{P}{t}$

  3. $E = \dfrac{{V}^{2}}{Rt}$

  4. None of these

Show answer
Correct Option: A
Explanation:

Electrical energy consumed by an electric appliance is equal to product of its power rating and time for which it is used $E = P \times t$.

When we pay for our electricity bill, we are paying for the:

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. charge used.

  2. current used.

  3. power used.

  4. energy used.

Show answer
Correct Option: D
Explanation:

Electricity bill is measured in units where 1 unit is equal to kWh which is the unit of energy. Hence, when we pay for our electricity bill, we pay for the amount of electrical energy consumed by us.

An electric kettle is rated as $2.5\ kW, \ 250\ V$. Find the cost running the kettle for two hours at $60\ \text{paisa}/\text{unit}$.

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $Rs\ 6$

  2. $Rs\ 3$

  3. $Rs\ 9$

  4. $Rs\ 1$

Show answer
Correct Option: B
Explanation:

Energy consumed, $E =2.5 \times 2 = 5\ kWh $
Cost, $C = 5 \times 0.60 = Rs\ 3 $

An electric bulb rated for $500$W at $100$ V is used in a circuit having a $200$V supply. The resistance R that one must put in series with the bulb, so that the power delivered in the bulb is $500$W is ______$\Omega$.

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $30$.

  2. $20$.

  3. $40$.

  4. $60$.

Show answer
Correct Option: B

Four bulbs, each of rating (100 W, 220 V) and connected in parallel across a voltage supply of 220 V, are operated for five hours daily. If all the bulbs are replaced by LEDs of rating (8 W, 220 V), how many units of electrical energy will be saved every month (30 days)? 

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. 55.2 units

  2. 60 units

  3. 4.8 units

  4. 32 units

Show answer
Correct Option: A
Explanation:

For bulbs :

$Energy\,\,=\,power\times time$

Total hours in 30 days $5\times 30=150hours$

So, $ energy=0.1\times 150=15J $

 $  $Power of 4 bulbs

 $ =4\times 15=60kW $

 $  $For LED:

Total hours in 30 days $=150hours$

$E=0.008\times 150=1.2J$

So, power of 4 LEDs $=1.2\times 4=4.8hours$

Saved energy 

  $ =\,\,60-4.8 $

 $ =55.2units $


How much energy in kilowatt hour is consumed in operating ten 50 watt bulbs for 10 hours per day in a month (30 days)

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. 1500

  2. 5000

  3. 15

  4. 150

Show answer
Correct Option: D
Explanation:

Energy consumed $=10\times 50\times 10\times 30\times 3600 J$
$[1 Kwh=3600\times 1000J]$
$=\frac {10\times 50\times 10\times 30\times 3600}{3600\times 1000}kWh=150$


A geyser of $2.5 kw$ is used for $8$ hours daily. Calculate the monthly consumption ( 30 days) of electrical energy units. Also calculate the cost of electricity units consumed in a month if rate per unit is $3.50$

physics effects of electric current thermal effect of electric current heating effect of electric current electric current and its effects

  1. $Rs. 2100.00$

  2. $Rs. 155.00$

  3. $Rs. 150.00$

  4. $Rs. 30.00$

Show answer
Correct Option: A
Explanation:

Daily usage of electricity   $E _1 = 2.5 \ kw\times 8 = 20 \ kwh = 20 \ units$

Energy used in one month   $E = 30E _1 = 30\times 20 = 600\ units$
Cost    $ = Rs. 600\times 3.5 = Rs 2100.00$