Electricity Past Paper PDF 2024-25

Solution The total energy consumed by the refrigerator in 30 days would be 400 W × 8.0 hour/day × 30 days = 96000 W h = 96 kW h Thus the cost of energy to operate...

Solution The total energy consumed by the refrigerator in 30 days would be 400 W × 8.0 hour/day × 30 days = 96000 W h = 96 kW h Thus the cost of energy to operate the refrigerator for 30 days is 96 kW h × Rs 3.00 per kW h = Rs 288.00 Q U E S T I O N S ? 1. What determines the rate at which energy is delivered by a current? 2. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h. What you have learnt n A stream of electrons moving through a conductor constitutes an electric current. Conventionally, the direction of current is taken opposite to the direction of flow of electrons. n The SI unit of electric current is ampere. n To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference across its terminals. It is measured in volts (V). n Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current. The SI unit of resistance is ohm (Ω). n Ohm’s law: The potential difference across the ends of a resistor is directly proportional to the current through it, provided its temperature remains the same. n The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor. n The equivalent resistance of several resistors in series is equal to the sum of their individual resistances. n A set of resistors connected in parallel has an equivalent resistance R p given by 1 1 1 1 = + + +... R p R1 R 2 R 3 n The electrical energy dissipated in a resistor is given by W=V×I×t n The unit of power is watt (W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V. n The commercial unit of electrical energy is kilowatt hour (kWh). 1 kW h = 3,600,000 J = 3.6 × 106 J. 192 Science 2024-25