Question

drive formula of heat energy in terms of V,I and R

Answer 1

Answer:

(a) When an electric charge Q moves against a p.d. V, the amount of work done is given by

W=Q×V ---------------(1)

We know, current , I=

t

Q

Q=I×t ------------(2)

By ohm's law ,

I

V

=R

V=I×R --------------(3)

Putting eqs. (2) and (3) in eq. (1),

W=I×t×I×R

W=I

2

Rt

Assuming that all the electrical work done is converted into heat energy , we get

Heat produced , H=I

2

Rtjoules

This relation is known as Joule's law of heating.

(b) Given : P=12W,V=12V,t=60sec

using the equation of power

P=VI

I=P/V=12/12=1A

The Ohm's law states that

V=IR

R=V/I=12/1=12ohm

The formula for heat is:

H=I

2

Rt

H=1

2

×12×60

H=720J

(c) The heat produced by the heater will become one - fourth because heat produced is directly proportional to the square of the current.

(d) When an electric current is passed through a high resistance wire , the wire becomes very hot and produces heat. This effect is known as heating effect of current. This effect is used in room heaters and electric ovens.

(e) Tungsten is used for making the filaments of an electric bulb.

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Answer 2

Answer:

W=Q×V                           ---------------(1)  

We know,  current , I=  

t

Q

​  

 

Q=I×t                                ------------(2)

By ohm's law ,  

I

V

​  

=R

V=I×R                             --------------(3)

Putting eqs. (2) and (3) in eq. (1),

W=I×t×I×R

W=I  

2

Rt

Assuming that all the electrical work done is converted into heat energy , we get

Heat produced , H=I  

2

Rtjoules

This relation is known as Joule's law of heating.

(b) Given : P=12W,V=12V,t=60sec

using the equation of power

P=VI

I=P/V=12/12=1A

The Ohm's law states that

V=IR

R=V/I=12/1=12ohm

The formula for heat is:

H=I  

2

Rt

H=1  

2

×12×60

H=720J