Advertisements
Advertisements
प्रश्न
When a resistance of 3Ω is connected across a cell, the current flowing is 0.5 A. On changing the resistance to 7Ω, the current becomes 0.25A. Calculate the e.m.f. and the internal resistance of the cell.
Advertisements
उत्तर
I = `"E"/("R + r")`
∴ `0.5 = "E"/(3 + "r")` ....(as I = 0.5 A when R = 3Ω)
∴ E = (3 + r) × 0.5 ....(i)
also 0.25 = `"E"/(7 + "r")` ...(as I = 0.25 A when R = 7 W)
∴ E = (7 + r) × 0.25 ....(ii)
Comparing equation (i) and (ii)
E = (3 + r) × 0.5
= (7 + r) × 0.25
∴ 1.5 + 0.5r = 1.75 + 0.25r
∴ 0.25 r = 0.25
Internal resistance = r = 1 Ω
Now E = I (R + r)
∴ E = 0.5(3 + 1) (as I = 0.5 A when R = 3 Ω, r = 1 Ω)
∴ E = 0.5 + 1.5 = 2 V
E.m.f. of cell E = 2 volt = 2 V.
संबंधित प्रश्न
What happens to the resistivity of semiconductor with the increase of temperature?
A cell is used to send current to an external circuit.
- How does the voltage across its terminals compare with its e.m.f.?
- Under what condition is the e.m.f. of a cell equal to its terminal voltage?
The diagram below in Fig. 8.40 shows a cell of e.m.f. ε = 2 volt and internal resistance r = 1 ohm 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, (ii) the key K is closed.
A battery of e.m.f 3.0 V supplies current through a circuit in which the resistance can be changed.
A high resistance voltmeter is connected across the battery. When the current is 1.5 A, the voltmeter reads 2.7 V. Find the internal resistance of the battery.
What is the colour code for the insulation on the earth wire?
Four cells, each of e.m.f. 1.5 V and internal resistance 2.0 ohms are connected in parallel. The battery of cells is connected to an external resistance of 2.5 ohms. Calculate:
(i) The total resistance of the circuit.
(ii) The current flowing in the external circuit.
(iii) The drop in potential across-the terminals of the cells.
A battery of 4 cell, each of e.m.f. 1.5 volt and internal resistance 0.5 Ω is connected to three resistances as shown in the figure. Calculate:
(i) The total resistance of the circuit.
(ii) The current through the cell.
(iii) The current through each resistance.
(iv) The p.d. across each resistance.
A cell supplies a current of 0.6 A through a 2Ω coil and a current of 0.3 A through on 8Ω coil. Calculate the e.m.f and internal resistance of the cell.
Explain the meaning of the term internal resistance of a cell.
The diagram in Figure shows a cell of e.m.f. ε = 4 volt and internal resistance r = 2 ohm connected to an external resistance R = 8 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
- the key K is open, and
- the key K is closed
