Question

(1) Two resistors of resistance 4 ohm and 6 ohm are connected in parallel to a cell to draw 0.5 A current from the cell.calculate the current in each resistor.
(2) A cell supplies a current of 1.2 A through 2 ohm resistors connected in parallel.When the resistors are connected in series,it supplies a current of 0.4 A.Calculate:
(i) the internal resistance,and
(ii) the e.m.f. of the cell

Answer 1

1. 4 ohm and 6 ohm are connected in parallel
so resultant resistance will be 1/r=1/4 + 1/6
=r=2.4 ohm  (24/(6+4))
applying ohm's law V=IR
I=0.5 A
V=0.5*2.4=1.2 v

in parallel connection voltage remains constant
current in 4ohm resistor=I=V/R
=1.2/4=0.3 A
current in 6 ohm resistor=1.2/6=0.2 A

2. how many resistors ? is it 2 2ohm resistors?
taking 2 2 ohm resistors
V=IR
=V=1.2*1 as current in parallel is 1.2 and 2 2 ohm resistors in parallel has net resistance as 1
=1.2 V

taking in series connection current is 0.4A and emf as 1.2V the internal resistance=V=IR
r=V/I=1.2/0.4=3 ohm

Answer 2

1. 4 ohm and 6 ohm are connected in parallel

so resultant resistance will be 1/r=1/4 + 1/6

=r=2.4 ohm  (24/(6+4))

applying ohm's law V=IR

I=0.5 A

V=0.5*2.4=1.2 v

in parallel connection voltage remains constant

current in 4ohm resistor=I=V/R

=1.2/4=0.3 A

current in 6 ohm resistor=1.2/6=0.2 A

2. how many resistors ? is it 2 2ohm resistors?

taking 2 2 ohm resistors

V=IR

=V=1.2*1 as current in parallel is 1.2 and 2 2 ohm resistors in parallel has net resistance as 1

=1.2 V

taking in series connection current is 0.4A and emf as 1.2V the internal resistance=V=IR

r=V/I=1.2/0.4=3 ohm