Which of the following electric device use minimum energy?
1. LED of 3 W used for 6 hours.
2. Water motor of 1 hp used for 20 mins.
3. Heater of 1200 W used for 30 mins.
4. Bulb of 60 W used for 1 hour.

To find that which electric device use minimum energy we need to find out the energy consumed by each appliance of a specific power rating for the given time.
 

 We have following information given-

First, we convert the power rating of all the appliance to a common unit (taking kilowatt) and time of all the appliance to a common unit (taking hour).

1. LED of 3 W used for 6 hours.

Power (P) = 3 W = 0.03 kw      $[\because 1W=\frac{1}{1000}kW]$

Time (t) = 6 h 

We know that-

$E=P\times T$                             [where, P = Power, and T = Time]

Substituting the value in the formula-

$E=0.03\times 6$

$E=0.18kW$

2. Water motor of 1 hp used for 20 mins.

Power (P) = 1 hp = 0.746 kw      $[\because 1hp=0.746kW]$

Time (t) = 20 m = 0.33 h              $[\because 1m=\frac{1}{60}h]$

We know that-

$E=P\times T$                                [where, P = Power, and T = Time]

Substituting the value in the formula-

$E=0.746\times 0.33$

$E=0.246kW$

3. Heater of 1200 W used for 30 mins.

Power (P) = 1200 W = 1.2 kw      $[\because 1W=\frac{1}{1000}kW]$

Time (t) = 30 m = 0.5 h                 $[\because 1m=\frac{1}{60}h]$

We know that-

$E=P\times T$                                [where, P = Power, and T = Time]

Substituting the value in the formula-

$E=1.2\times 0.5$

$E=0.6kW$

4. Bulb of 60 W used for 1 hour.

Power (P) = 60 W = 0.06 kw      $[\because 1W=\frac{1}{1000}kW]$

Time (t) = 6 h 

We know that-

$E=P\times T$                             [where, P = Power, and T = Time]

Substituting the value in the formula-

$E=0.06\times 6$

$E=0.36kW$

Now, we know the energy consumed by each appliance of a specific power rating for the given time. So, it will be easy to say which electric device uses minimum energy.

Energy consumption listed in descending order.

The electric device that uses minimum energy is LED of 3W used for 6 hours.

Tutorialspoint

Updated on: 10-Oct-2022

50 Views

Kickstart Your Career

Get certified by completing the course

Get Started