Electricity

Question 4:Figure 4 shows a circuit that is used to investigate the relationship between resistance, R and length of wire, l for two different wire conductors with the same diameter, that is 0.508 mm. Figure 5 shows the graph of resistance against length of wire.(a) What is meant by resistivity?(b) Based on the graph in … Read more

Question 1:Figure 1 shows a filament lamp. Why does a coiled filament produce a brighter light? Answer:– The filament lamps require high resistance to produce light.– The coiled filament causes the wire length to increase.– The resistance is directly proportional to the length of the wire.– The longer the filament wire, the higher the resistance.– … Read more

Question 1:The output power of a battery is 80 W. Determine the electrical energy that is supplied by the battery in: (a) 10 seconds(b) 2 hours Answer:(a) Power, P = 80 WTime, t = 10 sElectrical energy, E = Pt= 80(10)= 800 J(b) Power, P = 80 WTime, t = 2 h= 2 × 60 … Read more

Question 1:What is meant by electromotive force, e.m.f.? Answer:The electromotive force, e.m.f. is the energy transferred or work done by a source of electrical energy to move one coulomb of charge in a complete circuit. Question 2:State the difference between e.m.f. and potential difference. Answer:The electromotive force, e.m.f. is the work done by a source … Read more

Question 1:List the factors that affect the resistance of a wire. Answer:Wire length, cross-sectional area of wire, resistivity and temperature. Question 2:Calculate the total resistance of a coil of copper wire with a length of 50.0 m and a cross-sectional area of 2.5 mm2, given that the resistivity of copper at a temperature of 20°C … Read more

Question 1:Define current and potential difference. Answer:A current is the rate of flow of charge in a conductor.The potential difference is the work done to move one coulomb of charge between two points. Question 2:What is an electric field? Answer:An electric field is the region around a charged particle where any electric charge in the … Read more

Efficiency of Electrical Appliance The efficiency of an electrical appliance is given by the following equation Normally, the efficiency of an electrical appliance is less than 100% due to the energy lost as heat and the work done against friction in a machine. Example 1A lamp is marked “240V, 50W”. If it produces a light … Read more

Power Rating Figure above is an example of power rating label. An electrical appliance which is marked 240V, 1200W means that the electrical appliance will consume 1200J of energy in every second if the potential difference across it is 240V. ExampleA bulb rated 240V/80W is operated from a 120V power source. Find the resistance and … Read more

In a circuit of any connection (series or parallel), the power dissipated in the whole circuit is equal to the sum of the power dissipated in each of the individual resistor. Example 1:2 identical bulb of resistance 3Ω is connected to an e.m.f. of 12V. Find the power dissipated in the circuit ifa. the bulb … Read more