Electricity Past Paper Questions PDF

If a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is Q I = (11.1)...

If a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is Q I = (11.1) t The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 1018 electrons. (We know that an electron possesses a negative charge of 1.6 × 10–19 C.) The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836). One ampere is constituted by the flow of one coulomb of charge per second, that is, 1 A = 1 C/1 s. Small quantities of current are expressed in milliampere (1 mA = 10–3 A) or in microampere (1 µA = 10–6 A). An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured. Figure 11.1 shows the schematic diagram of a typical electric circuit comprising a cell, an electric bulb, an ammeter and a plug key. Note that the electric current flows in the circuit from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter. Figure 11.1 A schematic diagram of an electric circuit comprising – cell, electric bulb, ammeter and plug key Example 11.1 A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit. Solution We are given, I = 0.5 A; t = 10 min = 600 s. From Eq. (11.1), we have Q = It = 0.5 A × 600 s = 300 C Q U E S T I O N S 1. 2. 3. What does an electric circuit mean? Define the unit of current. Calculate the number of electrons constituting one coulomb of charge. ? 172 Science 2024-25