Advertisements
Advertisements
Question
An immersion rod having resistance of 50 Ω is connected to 220V main supply. Assuming that all the energy generated goes to heat the water, calculate the time taken to heat 5 kg water from 30°C to 100°C.
Advertisements
Solution
We know that P = VI
∴ I = `"P"/"V" = 220/50 = 4.4`
Heat produced in an immersion heater
H = I2Rt
H = (4.4)2 × 50 × t
H = 968 t Joules
and Heat needed = mcθ
where C is the sp. heat capacity of water
= 4.2 × 103 J/kgC = 5 × 4.2 × 103 × (100 - 30)
= 5 × 4.2 × 103 × 70 = 1470000 J.
But Heat lost = Heat gained
968 t = 1470000
t = `1470000/968`
t = 1518.59 secs
t = 1518.6 secs
t = 25.326 min.
t = 25.33 mins.
RELATED QUESTIONS
Name the physical quality which is measured in
(i) Kw (ii) kWh
A simple electric circuit has 24 V battery and a resistor of 60 Ω. What will be the current in the circuit? The resistance of the connecting wires is negligible.
An electric iron rated 750 W is operated for 2 hours/day. How much energy is consumed by the electric iron for 30 days?
Mention three uses of the carbon arc.
Why is a concave reflector placed behind the heating element in a room heater.
You are required to connect a bulb, a fan and a socket outlet to the mains in one set A and an air-conditioner and a refrigerator to the mains in other set B. Will you recommend the wire of same thickness and same insulation in both? explain your answer.
An electric kettle is rated 3kW, 250V. What should be the current capacity of the fuse with it?
An electric lamp A of 40 W and another electric lamp B of 100 W are connected to 220 V supply. Calculate the ratio of their filament resistances?
A house is provided with 15 bulbs of 40W, 5 bulbs of 100W, 5 fans of 80 W, and one heater of 1.0 kW. Each day bulbs are used for 4h, fans for lOh, and heater for 2h. The voltage of mains is 220 V. Calculate:
(i) Maximum power of the circuit in the house,
(ii) maximum current capacity of the main fuse in the house,
(iii) the electrical energy consumed in a week,
(iv) cost of electricity consumed at 1.25 Rs. per kWh.
A student wants to use an electric heater, an electric bulb and an electric fan simultaneously.
How should these gadgets be connected with the mains? Justify your answer giving three reasons.
