An electric kettle taking 3 . 5 A at 210 V brings 1200 c . c . of water from 25 ° C to 95 ° C in 12 min . Find the percentage of energy supplied which goes towards heating water.

Total Heat energy supplied by kettle H s = P × t Where, P = Power, t = time H s = 210 × 3 . 5 × 12 × 60 J Now, Heat energy used by water H = m × c × ∆ t Where, m = Mass of water, c = Specific heat of water, ∆ t = 95 - 25 = 70 H= 1200 × 10 - 6 × 1000 × 4200 × 70 H = 12 × 10 3 × 10 3 × 10 - 6 × 4200 × 70 H = 12 × 7 × 4200 J Percentage of energy supplied by water = H H s × 100 12 × 4200 × 7 210 × 3 . 5 × 12 × 60 × 100 = 66 . 7 %

When the cold junction of an aluminium-lead thermocouple is maintained at 0 ° C , the thermo-emf E of this thermocouple has the corresponding dependence given by the relation E = - 0 . 76 θ + 1 2 ( 0 . 0039 ) θ 2 × 10 - 6 where E is in volts and θ is the temperature of the hot junction, in C ∘ . Find the neutral temperature for this thermocouple.

E = - 0 . 76 θ + 1 2 ( 0 . 0039 ) θ 2 × 10 - 6 Comparing the given equation with standard equation E = αt + 1 2 βt 2 Therefore, α = - 0 . 76 , β = 0 . 0039 Hence, neutral temperature t n = - - 0 . 76 0 . 0039 = 194 . 87 ° C

MEDIUM

12th West Bengal Board

IMPORTANT

Earn 100

A $5$ H.P. electric motor working on $220 V$ mains runs for $8$ hours a day. If electricity is rated Rs $2.40$ a unit, find the cost of running it for $30$ days. Also find the current through the motor when running on full capacity.

Important Questions on Thermal Effect and Chemical Effect of Current

MEDIUM

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 11

A certain quantity of water in an electric kettle begins to boil

15

min after the kettle is switched on. The heating element consists of a coil of wire

5 m

long. By how much should the length of the heating element be increased or decreased in order that the same quantity of water in the kettle to boil

12

min after the kettle is switched on? Neglect heat loss to the surroundings.

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 12

The burner of an electric stove is made up of three sections of equal resistances. If the three sections are connected in parallel water in a tea-kettle begins to boil in

6

minutes. When will the same mass of water in the tea kettle begins to boil if the sections are connected in series?

EASY

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 13

In order for a

60 V, 120 W

lamp to work at its full when inserted in

220 V

d.c. line, a resistor of what magnitude should be placed in series with it?

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 14

An electric kettle taking

3.5 A

210 V

brings

1200 c . c .

of water from

25 ° C

95 ° C

12 \min

. Find the percentage of energy supplied which goes towards heating water.

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 15

A constant current of

1 A

flows through a platinum wire of resistance

5

ohm stretched along the axis of a cylindrical tube through which a steady stream of water passes at a rate of

15 c m^{3}

per minute. The steady difference between the temperature of the water entering and leaving the tube is

4.8 ° C

. Neglecting losses of heat, calculate the mechanical equivalent of heat.

EASY

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 16

In a household, the supply voltage is

220 V

. The circuit includes a

1200 W

toaster,

1000 W

oven,

800 W

heater and

1500 W

cooler. The line has been made with a heavy duty wire and includes a

20 A

circuit breaker. Will the circuit breaker snap if all the equipments are used simultaneously?

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 17

If for a certain thermocouple,

E = at + {bt}^{2},

where t is the temperature of the hot junction, the cold junction being at

0 ° C, a = 10 μ V ° C^{- 1}

and

b = - \frac{1}{40} μV ° C^{- 2}

find the neutral temperature and the temperature of inversion.

MEDIUM

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 6 - Thermal Effect and Chemical Effect of Current>EXERCISE 6>Q 18

When the cold junction of an aluminium-lead thermocouple is maintained at

0 ° C

, the thermo-emf E of this thermocouple has the corresponding dependence given by the relation

E = \{- 0.76 θ + \frac{1}{2} (0.0039) θ^{2}] \times 10^{- 6}

where E is in volts and

θ

is the temperature of the hot junction, in

{}^{\circ}C

. Find the neutral temperature for this thermocouple.

A 5 H.P. electric motor working on 220 V mains runs for 8 hours a day. If electricity is rated Rs 2.40 a unit, find the cost of running it for 30 days. Also find the current through the motor when running on full capacity.

Important Questions on Thermal Effect and Chemical Effect of Current

Learn and Prepare for any exam you want !

A $5$ H.P. electric motor working on $220 V$ mains runs for $8$ hours a day. If electricity is rated Rs $2.40$ a unit, find the cost of running it for $30$ days. Also find the current through the motor when running on full capacity.