Question

A 800 W electrical device is designed to work at 200 V. What will be its power if the device is working at 100 V?

Answer 1

The quantity of energy transported or transformed per unit time is referred to as power in physics. The watt, which is equal to one joule per second in the International System of Units, is the unit of power. Power is also referred to as activity in earlier texts. A scalar quantity is power. The product of the torque generated by a motor and the angular velocity of its output shaft is the motor's output power.

Formula used
$P\text{ }=\text{ }V\text{ }I$
P = Power
V = Potential Difference
I = Current

Complete step by step solution:
Electric power is the rate at which electrical energy is transmitted by an electric circuit per unit of time. The watt, or one joule per second, is the SI unit of power. Electric generators are the most common source of electricity, however other sources such as electric batteries can also be used. The electric power sector often provides it to companies and residences (as residential mains electricity) via an electric power grid. Transmission lines can transport electric power across vast distances and be utilised for high-efficiency applications including motion, light, and heat.
Given a 800 W electrical device is designed to work in 200 V.
$P\text{ }=\text{ }V\text{ }I$
$800\text{ }=\text{ }200\text{ }I$
$I\text{ }=\text{ }4\text{ }A$

So, What will be its power if the device is working at 100 V?
$P\text{ }=\text{ }V\text{ }I$
$P\text{ }=\text{ }100\text{ }x\text{ }4$
$P\text{ }=\text{ }400\text{ }W$

Note: It's important to remember that power is a scalar number. When electric charges flow across an electric potential difference (voltage), which happens in electrical components in electric circuits, they are converted to various kinds of energy. Components in an electric circuit can be classified into two groups in terms of electric power.