P1-Chapter 2 Using Energy Flashcards
Where does the chemical energy stored in your muscles come from?
From the food that you eat
Kinetic energy
Energy of a moving object due to its motion; kinetic energy (in joules, j) = 1/2 X mass (in kilograms, kg) X (speed)2 (in m2/s2)
Electrical energy
Energy transferred by the movement of electrical charge
Gravitational potential energy
Energy of an object due to its position in a gravitational field. Near the earths surface, change of GPE (in joules,j) =weight (in newtons,N) X vertical distance moved (in metres, m)
Elastic potential energy
Energy stored in an elastic object when work is done to change its shape
Chemical energy
Energy of an object due to chemical reactions in it
What energy transfers take place when you turn on a torch?
Chemical to electrical to light and transfer by heating
In terms of energy, what happens when you burn a fuel?
Chemical energy in the fuel is transferred to the surroundings, which get warmer
Conservation of energy
Energy cannot be created or destroyed
What happens to the wasted energy from a light bulb?
It is transferred to the surroundings which get warmer
Why should we talk about energy being ‘wasted’ not energy being ‘lost’?
Because the law of conservation tells us that energy cannot be destroyed
What is the equation to calculate efficiency of any appliance that transfers energy?
Efficiency= useful energy transferred by the appliance divided by total energy supplies to the appliance (x100)
In a lightbulb, for every 25 Joules of energy that are supplied to the bulb, 5 joules are usually transferred into light energy. What is the efficiency of the bulb?
The efficiency is 0.2 or 20%
A machine is adjusted so that it wastes less energy because of friction. What happens to the efficiency of the machine?
The efficiency increases
Efficiency
Useful energy transferred by a device divided by total energy supplies to the device
What form of energy does a moving car have?
Kinetic energy
What form of energy does a stretched Spring have?
Elastic potential energy
When is electrical energy transferred?
When an electrical current flows
What are the useful energy transfers that take place in a hairdryer?
Electrical energy to kinetic energy and energy transferred by heating
What energy transfers take place when you lift a ball into the air and then drop it so it falls to the ground?
Kinetic energy to gravitational potential energy to kinetic energy
What form of energy does a compressed Spring have?
Elastic potential energy
What are the useful energy transfers that take place in a television?
Electrical energy to light and sound
Wear and tears cause a particular machine to waste more energy. What happens to the efficiency of this machine?
It’s efficiency decreases
In an electric motor, 250 J of energy are transferred to the surroundings by heating, for every 1000 J of electrical energy supplies. What is the efficiency of the motor as a fraction?
Efficiency of the motor is 3/4 or 0.75 or 75%
Why is an electric heater the only appliance that may have an efficiency of 1 or 100%?
Because it is designed to transfer energy by heating, which is normally how appliances waste energy
Why do electrical appliances such as television and computers have vents?
So that wasted energy can be transferred easily to the surroundings making them warmed, rather than the television or computer
60J of energy are supplied each second to a light bulb. The bulb transfers 18 J of energy to light each second. How much energy does the bulb waste each second?
42 J
When a kettle full of cold water is brought to boiling point, 720 000 J of energy are transferred to the water. If the kettle has an efficiency of 96% how much energy is supplied to the kettle to boil the water?
750 000 J
