National Physics Electricity and Energy Homework Section 2 Electrical Power
Homework 1 : Energy Changes and Power 1. Appliances convert electrical energy into other forms of energy. State the useful energy output from the following appliances. a) Lamp: electrical energy... energy (1) b) Kettle: electrical energy... energy (1) c) Hair dryer: electrical energy energy +. energy (2) d) Food processor: electrical energy... energy (1) e) Television: electrical energy energy +. energy (2) 2. From the following household appliances: Electric Oven, Food Mixer, Flat screen TV, DVD player. a) Which household appliance would have the highest power rating? (1) b) Give a reason for your answer. (1) 3. A student makes a statement: The power of a light bulb is 60 W. What does this statement mean in terms of energy? (1) Homework 2 : Power, Energy and Time 1. How long will it take a 1.2 kw vacuum cleaner to use up 720 kj of electrical energy? (3) 2. What is the power of a radio that uses up 27 kj of electrical energy in five minutes? (3) 3. A 725 W fridge is switched on for one day? a) Calculate the number of seconds in one day. (1) b) Calculate how much energy is used by the fridge in one day. (3)
Homework 3 : Power, Current and Voltage 1 1. Calculate the voltage across a 24W lamp when the current is 2A. (3) 2. Calculate the power of the resistor in the following circuit. (3) 6V A 0.1A 3. State the rated mains voltage in the United Kingdom. (1) 4. A 20 Watt light bulb is used to light up a room in a house. Calculate the current drawn by the light bulb. (3) Homework 4 : Power, Current and Voltage 2 1. Calculate the power dissipated in the 1kΩ resistor in the circuit shown below if the voltage across the variable resistor is 8V. (3) 12V V 4V 4mA R V 1kΩ 2. Three 40 W light bulbs are connected in parallel with the mains power supply, as shown. 230 40 W 40 W 40 W a) What is the total power of the 3 lamps? (1) b) What is the current drawn from the mains? (3) c) What is the current flowing through one single bulb? (3)
Homework 5 : Power, Current and Resistance 1 1. Combine the equations P = IV and ohms law (V=IR) to derive the equation (1) 2. What is the power rating of a lamp that has a resistance of 5 Ω and a current of 1.2A flowing through it? (3) 3. What is the current flowing through a 50 Ω heating element in a toaster if it has a power rating of 800 W? (3) 4. What is the resistance of a 1200 W electric convection heater that has a current of 5.0 A flowing through it? (3) Homework 6 : Power, Current and Resistance 2 12V 3000Ω 1000Ω 1. For the above circuit find: a) The total resistance of the circuit. (1) b) The current flowing through each resistor. (3) c) The power dissipated in the 3000Ω resistor. (3) 2. Two identical bulbs are connected as shown below. They each have a resistance of 20 Ω. The supply current is shown. Calculate the power of bulb 2. (3) 0.5A Bulb 1 Bulb 2
Homework 7 : Power, Voltage and Resistance 1. Combine the equations P = IV and ohms law (V=IR) to derive the equation 2. A circuit is set up as shown. (1) Calculate the power supplied to the resistor. (3) 3. Calculate the power supplied to the 40Ω resistor in the following circuit. (3) 6V 20Ω 40Ω V 2V 4. Calculate the resistance of a 1200W kettle which is plugged into the mains supply. (3)
Homework 8 : Fuses, Plugs and Domestic Wiring 1. A fuse in contained in all electrical plugs. a) What is the purpose of a fuse? (1) b) Explain how it works. (1) 2. Copy and complete the following table. Write a typical power rating for each appliance (you could check the appliances in your home or check the internet), then use your knowledge of fuses to state the correct value of fuse for each appliance. Appliance Power rating Fuse Rating Television Lamp Hoover Iron 3. Label the diagram of the three pin plug shown below. (2) (2) 4. The following circuits are found in a typical house. a) Fully name the type of circuit A. (1) b) Fully name the type of circuit B. (1) c) State 2 advantages of circuit B. (Hint: Write one advantage about current). (2) 230V a.c Earth Neutral Live Circuit A Circuit B