An electric bulb, connected to a make and break power supply, switches off and on every second in its rest frame. What is the frequency of its switching off and on as seen from a spaceship travelling at a speed 0.8c?

Statement-1: Knowing that rating is done at steady state of the filament, an electric bulb connected to a source having rated voltage consumes more than rated power just after it is switched on. Statement-2: When filament is at room temperature its resistance is less than its resistance is less than its resistance when the bulb is fully illuminated

A liquid having mass m = 250 g is kept warm in a vessel by use of an electric heater. The liquid is maintained at 50^(@)C when the power supplied by heater is 30 watt and surrounding temperature is 20^(@)C . As the heater is switched off, the liquid starts cooling and it was observed that it took 10 second for temperature to fall down from 40^(@)C to 39.9^(@)C . Calculate the specific heat capacity of the liquid. Assume Newton’s law of cooling to be applicable.

An electric tungsten bulb is connected into a home circuit. The home electric supply runs at 220 V potential difference. When switched on, a current of 0.45 A flows through the bulb What must be power (wattage)of the bulb? if it is kept on for 10 hours, how many units of electricity will be consumed?

An electric tungsten bulb is connected into a home circuit. The home electric supply runs at 220 V potential difference. When switched on, a current of 0.45 A flows thorugh the bulb. What must be power (wattage) of the bulb? If it is kept on for 10 hours, how many units of electricity will be consumed?

An electric motor of power 75 W rotates a flywheel of moment of inertia 0.36 kg - m^(2) at a constant rate of 100 rad s^(-1) . If the power is switched off, the time taken for the wheel to come to rest is

A metal block is placed in a room which is at 10^(@)C for long time. Now it is heated by an electric heater of power 500 W till its temperature becomes 50^(@)C . Its initial rate of rise of temperature is 2.5^(@)C//sec . The heater is switched off and now a heater of 100W is required to maintain the temperature of the block at 50^(@)C . (Assume Newtons Law of cooling to be valid) What is the rate of cooling of block at 50^(@)C if the 100W heater is also switched off?

A metal block is placed in a room which is at 10^(@)C for long time. Now it is heated by an electric heater of power 500 W till its temperature becomes 50^(@)C . Its initial rate of rise of temperature is 2.5^(@)C//sec . The heater is switched off and now a heater of 100W is required to maintain the temperature of the block at 50^(@)C . (Assume Newtons Law of cooling to be valid) What is the rate of cooling of block at 50^(@)C if the 100W heater is also switched off?

An electric heater of resistance 10Omega connected to 220 V power supply is immersed in the water of 1 kg. How long the electrical heater has to be switched on to increase its temperature from 30^(@)C to 60^(@)C . (The specific heat of water is s=4200J kg^(-1) /C )