Advertisements
Advertisements
Question
A cell supplies a current of 1.2 A through two 2Ω resistors connected in parallel. When the resistors are connected in series, if supplies a current of 0.4 A. Calculate the internal resistance and e.m.f of the cell.
Solution
(i) The effective resistance of a circuit with two 20-ohm resistors linked in parallel is R is `1/"R" = 1/2 + 1/2`
∴ R = 1Ω
'r' stands for the internal resistance of the cell that is in series with the circuit.
∴ V = IR
or V = 1.2 (1 + r) ...(i)
Connected in series, the effective resistance of the two resistors and the cell's internal resistance, denoted as 'r'
R = 2 + 2 + r
= (4 + r) Ω ...(ii)
V = IR
= 0.4 (4 + R)
(i) = (ii)
1.2 (1 + r) = 0.4 (4 + r)
1.2 + 1.2 r = 1.6 + 0.4 r
or (1.2 - 0.4) r = (1.6 - 1.2)
0.8 r = 0.4
r = `0.4/0.8`
= `1/2`
= 0.5 Ω
put r = 0.5 in (i)
(ii) e.m.f. of cell E = V = 1.2 (1 + 0.5) = 1.8 V
APPEARS IN
RELATED QUESTIONS
A wire that has resistance R is cut into two equal pieces. The two parts are joined in parallel. What is the resistance of the combination?
Explain with diagram what is meant by the "series combination" and "parallel combination" of resistances. In which case the resultant resistance is : (i) less, and (ii) more, than either of the individual resistances?
A resistor of 8 ohms is connected in parallel with another resistor X. The resultant resistance of the combination is 4.8 ohms. What is the value of the resistor X?
Five resistors, each 3 Ω, are connected as shown in Fig. Calculate the resistance
- between the points P and Q.
- between the points X and Y.
In the following figure calculate:
- the total resistance of the circuit
- the value of R, and
- the current flowing in R.
A particular resistance wire has a resistance of 3 ohm per meter. Find :
The total resistance of three lengths of this wire each 1.5 m long, in parallel.
How does the resistance of a metallic wire depend on the thickness of wire?
A piece of wire of resistance R is cut into three equal parts. These parts are then connected in parallel. If the equivalent resistance of this parallel combination is R1, what is the value of the ratio R1 : R?
Four resistors each of resistance 5 Ω are connected in parallel. What is the effective resistance?
