[PHY] Chapter 19 - Practical Electricity

DARRELL ER (COPYRIGHTED) © TOPIC 19: PRACTICAL ELECTRICITY DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

HEATING EFFECT OF ELECTRICITY APPLICATIONS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

HEATING EFFECT When current flows through a circuit, it may create a heating effect due to the resistance of the components. Heating element are usually made of nichrome wire coiled around an insulating fireproof material. Nichrome is the most commonly used due to: - high resistance, therefore heats up quickly - high melting point - does not oxidise or rust easily APPLICATION Electric Kettle The heating element is enclosed in a metal tube and when a current flows through the heating element, the water around the element is heated by conduction and thermal energy is then transferred throughout the fluid by convection. Electric Iron Thermal energy produced is spread evenly over a large metal base which conducts thermal energy well. Electric irons usually contain a thermostat which switches the current off when it gets too hot and switches it back on when the iron cools below selected temperature. HEATING EFFECT OF ELECTRICITY Nichrome is commonly used in ovens as well! DARRELL ER (COPYRIGHTED) ©

ENERGY SOURCES ELECTRICAL POWER ELECTRICITY CONSUMPTION KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

ENERGY SOURCES Renewable Energy Non-Renewable Energy Pros Cons Pros Cons Solar Energy Harnessing free energy. Does not produce greenhouse gas. Solar panels are still rather expensive and inefficient. Wind Energy Harnessing free energy. Does not produce greenhouse gas. Wind farms take up a lot of land and is inefficient. Hydroelectric Energy Harnessing free energy. Does not produce greenhouse gas. Affects aquatic life. May cause flooding downstream. Fossil Fuels Cheaper. Fossil fuels produce large amount of greenhouse gas. Air pollution due to ash. Nuclear Energy Does not produce greenhouse gas. Nuclear waste is hard to store. SUMMARY TABLE DARRELL ER (COPYRIGHTED) ©

ELECTRICAL POWER Electrical power is defined as the rate at which electrical energy is converted to other forms of energy due to the circuit components. Units: Watts (W) P = E / t Where, P = Power E = Energy converted t = time 2R P = V2 / R ELECTRICAL POWER When we buy light bulbs, there’s usually a rating like ‘230V, 40W’. This means that the light bulb has a potential difference of 230V. Each charge is required to ‘deposit’ 230 J of electrical energy to go across the component. The 40W means that for the light bulb to produce light, 40 J of electrical energy is used per second. If we apply P = VI, we can then derive that for the light bulb to operate, it needs to draw a current of 0.17A. (Since each charge brings 230J while only 40J is consumed each second, only 0.17 charge needs to flow per s