Joule Heating

Q.

A student boils the water in an electric kettle for 20 minutes. Using the same main supply, he wants to reduce the boiling time of water. To do so, should he increase or decrease the length of the heating element? Justify your answer

Q.

When the current I in electric circuit is tripled, the heat energy H generated becomes __ the original heat energy generated.

1. 1.5 times

2. 6 times

3. 27 times

4. 9 times

Q. What is the difference between electric power, electrical energy, heat produced by a conductor on current being passed through it?

Q. When the electric current increases, does the resistance increases or decrease?

Q.

An electric heater of power 3 kW is used for 10 hours. How much energy does it consume? Express your answer in (i) kWh, (ii) joule.

Q.

What will be the percentage change in generated heat of a heating coil if the current through the coil is halved and the length of the coil is doubled for an unit time.

1. 20%

2. 50%

3. 40%

4. 46%

Q.

An electrical appliance is rated at $1000KVA,220V.$ If the appliance is operated for $2$ hours, calculate the energy consumed by the appliance in:
$Joule$

Q. A current of 0.4 A is flowing through a conductor having resistance of 100 Ω. It generates a heat of 1200 J. For how much time the current is flowing through the conductor?

1. 65 s
2. 75 s
3. 75 min
4. 85 s

Q. Question 14
An electric heater is rated 1500 W. How much energy does it use in 10 hours?

Q.

Heat generated in current carrying conductor___.

1. is inversely proportional to I²

2. is directly proportional to R²

3. is directly proportional to I²

4. is inversely proportional to R²

Q.

Assertion(A): A $200$W bulb consumes $2$ units of electrical energy when it is used for $10$ hours.

Reason(R): $1$ unit of electrical energy $=1000$ kWh.

1. (A) and (R) are correct and (R) is the correct explanation for (A)

2. (A) and (R) are correct but (R) is not the correct explanation for (A)

3. (A) is correct but (R) is not correct

4. (A) is not correct but (R) is correct

Q. Three heaters each rated $250W$, $100V$ are connected in parallel to a $100V$ supply. The energy supplied in $kWh$ to the three heaters in $5hours$ is :

1. $5.74kWh$
2. $0.6kWh$
3. $3.75kWh$
4. $4kWh$

Q. The correct relation between heat produced (H) and electric current is
H is proportional to I
H is inversely proportional to I
H is proportional to I^{​​​​​​2}
H is inversely proportional to. I^{​​​​​​2}

Q.

When a 0.5 kW heater operates for 20 minutes, the electrical energy consumed is equal to ___kJ.

1. 200 kJ

2. 400 kJ

3. 600 kJ

4. 800 kJ

Q. A light bulb has a power rating of $1kW$ which converts about $10$ % electrical energy into visible light. If energy other than visible is waste energy. How many kilo-joules does a light bulb wasted in one hour?

1. 90 kJ
2. 3240 kJ
3. 36 kJ
4. 360 kJ
5. 32, 400 kJ

Q. The electrical energy in kilowatt hours consumed in operating ten $50W$ bulbs for $10hrs/day$ in a month of $30days$ is

1. $1500$
2. $15000$
3. $150$
4. $15$

Q.

Determine the heat energy generated in terms of kJ in an induction stove when a current of 8 A passes through its coils for 5 min when applied voltage is 230 V.

1. 525 kJ

2. 552 kJ

3. 55.2 kJ

4. 55200 kJ

Q. Question 3
An electric iron of resistance $20\Omega$ takes a current of 5 A. Calculate the heat developed in 30 s.

Q. If the electric current in a lamp decreases by $5\%$, then the power output decreases by:

1. $20\%$
2. $10\%$
3. $2.5\%$
4. $5\%$

Q.

A heating coil has a resistance of $200\Omega$ . At what rate will heat be produced in it when a current of 2.5 A flows through it?

Q.

Determine the value of time t, when heat H = 64 J, current I = 2 A and resistance R = 4 ohm.

1. 0.4 s

2. 40 s

3. 4 ms

4. 4 s

Q. Calculate the power of soldering iron with a hot resistance $4$ $K\Omega$ and operating voltage of $200$ $V$.

Q. State whether true or false :
In order to increase the area absorbing heat energy, coil shaped copper tube is used.

1. true
2. false

Q.

Calculate value of heat H generated when voltage = 10 volts, current = 2 A and time = 5 s.

1. 10 J

2. 1 kJ

3. 100 J

4. 1 J

Q. When a current of 4.0 A passes through a certain resistor for 10 minutes, 2.88 × 10⁴ J of heat are produced. Calculate

(a) the power of the resistor.
(b) the voltage across the resistor.