Question

this my Question IF external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is
(a) 30 V (b) 60V (c) 50 V (d) 40 V

Answer 1

Answer:

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Answer 2

Given : External resistance connected to a cell has been increased to 5 times ,  the potential difference across the terminals of the cell increases from 10 V to 30 V.

To Find :  the emf of the cell  

• (a) 30 V
• (b) 60V
• (c) 50 V
• (d) 40 V

Solution:

E - Ir  = V

V = IR

r = internal Resistance

R = external Resistance

I  = E/(R + r)

V = 10  V

=> E - Er/(R + r)  = 10

=> ER + Er - Er = 10R + 10r

=> ER = 10R + 10r

Now V = 30 V   and R = 5R

=>  E - Er/(5R + r)  = 30

=> 5ER + Er - Er = 150R + 30r

=> 5ER = 150R + 30r

=> 5(10R + 10r) = 150R + 30r

=> 50R + 50r = 150R + 30r

=> 20r  = 100R

=> r = 5R

ER = 10R + 10r

=> ER = 10R + 10(5R)

=> ER = 60R

=> E = 60

the emf of the cell is 60 V

Correct option is b) 60 V

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