A cell of emf 1V and internal resistance r = 1ohm is connected to an external resistance R = 4ohm. The ammeter A measures the current in the circuit and the voltmeter V measures the terminal voltage across the cell. What will be the readings of the ammeter and voltmeter when: (i) the key K is open, (ii) the key K is closed.

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Solution

Dear Student,

$r = 1 o h m (i n t e r n a l r e s i s \tan c e o f c e l l .) . R = 4 o h m (E x t e r n a l R e s i s \tan c e o f c i r c u i t) . E = 1 v (E M F o f c e l l .) . C a s e 1) o p e n k e y : n o c u r r e n t w i l l f l o w w h e n k e y i s o p e n, s o t h e r e w o n t b e a n y r e a d i n g i n a m e t e r a n d b o l t m e t e r . C a s e 2) C l o s e d k e y : c u r r e n t I w i l l f l o w t h r o u g h t h e c i r c u i t . L e t v b e t h e p o t e n t t i a l d i f f e r e n c e a c r o s s t h e t e r m i n a l . V = E - I r . I R = E - I r . I \times 4 = 1 - I \times 1 I = \frac{1}{5} = 0.2 A . V = E - I r = 1 - 0.2 \times 1 = 0.8 v . A n s) . . T h e a m e t e r w i l l r e a d 0.2 A a n d t h e v o l t m e t e r w i l l r e a d 0.8 V .$

Regards.

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The diagram in the figure shows a cell of e.m.f. $ε = 2$ volt and internal resistance r = 1 ohm connected to an external resistance R = 4 ohm. The ammeter A measures the current in the circuit and the voltmeter V measures the terminal voltage across the cell. What will be the readings of the ammeter and voltmeter when (i) the key K is open, and (ii) the key K is closed?