A resistance R is connected across a cell with a switch and a rheostat in series. A voltmeter is connected parallel across the cell. Current in the circuit is increased using the rheostat.
(a) How will the voltmeter reading change? (increase / decrease / remain the same)
(b) Justify your answer stated in (a) above.
(a) The voltmeter reading decreases.
(b) The voltmeter reading is given by: V = ε – Ir
where I is the current flowing in the circuit, ε is the emf of the cell and r is the internal resistance of the cell.
When the rheostat is adjusted to increase the current in the circuit, the current drawn from the cell becomes larger. Due to the internal resistance of the cell, a greater potential drop occurs inside the cell.
As a result, the terminal voltage of the cell decreases. Since the voltmeter measures this terminal voltage across the cell, its reading decreases.
More ICSE Easy level questions
5 bulbs are connected in series in a room. One bulb is fused. It is removed and remaining 4 bulbs are again connected in series to the same circuit. What will be the effect on the following physical quantities? (Increases, Decreases, Remain Same) (a) Resistance (b) Intensity of light
A current flows through a metallic conductor for a long period of time. State the change you would expect in its: (a) Resistance (b) Resistivity
‘A geyser is rated 240 W – 220 V’. Explain the meaning of this statement.
Study the diagram: (a) Calculate the total resistance of the circuit. (b) Calculate the current drawn from the cell. (c) State whether the current through 10 Ω resistor is greater than, less than or equal to the current through the 12 Ω resistor.
The specific resistance of a wire depends on: (a) its length (b) the material of the wire (c) its cross-sectional area (d) its radius
When a current I flows through a wire of resistance R for time t then the electrical energy produced is given by: (a) I2Rt (b) IR2t (c) IRt (d) IRt2
Find the value of current I drawn from the cell. (a) Calculate the current I. (b) Calculate the terminal voltage.
The potential difference between the terminals of a cell in a closed circuit is called: (a) terminal voltage (b) electromotive force (c) voltage drop (d) none of these
Three identical bulbs B1, B2 and B3, each of power rating 18 W, 12 V, are connected to a battery of 12 V as shown. (a) Calculate: (i) the resistance of each bulb (ii) the current drawn from the cell (b) If bulb B3 is removed from the circuit, will the brightness of bulb B1 increase, decrease or remain the same?
In a closed circuit containing a bulb and a cell, the electromotive force (ε) and the terminal voltage (V) is related as. (Given I is current and r is internal resistance.) (a) V = ε + Ir (b) V = ε – Ir (c) V = ε ÷ Ir (d) V = ε × Ir
Choose the correct relation for e.m.f. (ε) and terminal voltage V: (a) ε = V [always] (b) V > ε [always] (c) V < ε [when the cell is in use] (d) None of these
(a) Define specific resistance. (b) What happens to the specific resistance of a conductor if its length is doubled? (c) Name a substance whose specific resistance remains almost unchanged with the increase in its temperature.
