Energy transfer by appliances: power, everyday appliances, static electricity, electric fields Flashcards
what is the energy transfer in blenders and fans
electrical energy to kinetic energy of the electric motors
blender moves to mix food
fan moves to create air currents
small amount of electrical energy is transferred to thermal energy due to friction in the motors
what is the energy transfer in the iron and the kettle
both appliances transfer electrical energy into thermal energy
some appliances are designed to transfer electrical energy into both thermal energy and kinetic energy
-hairdryer
-washing machine
both of these appliances use electrical energy both of them transfer the electrical energy into thermal energy and kinetic energy of the electric motors
a motor moves air through the hairdryer and heating element heats the air
washing machine- heating element heats the water and a motor turns the drum to wash the clothes
what is power definition
power is the rate at which energy is transferred 1 watt is an energy transfer of 1J per second
for example a blender has a power rating of 400w meaning it transfers 400 joules of energy per second
A kettle has a power rating of 2200 watts and is used for 80 seconds. calculate the total energy transferred
E= power (watts) x time (seconds)
2200x80= 176000J
176KJ
A fan has a power rating of 20 watts and is used for 1 hour. calculate total energy transferred
energy= power (watts) x time (seconds)
20 x 3600=72000
72KJ
An iron is used for five minutes and a total of 600,000 joules of energy is transferred. calculate the power of the iron
power (watts)= energy (joules) / time (seconds)
600,000 divided by 300= 2000 watts
A blender has a power of 400 watts and a total of 48,000 joules of energy is transferred when the blender is in use. calculate the time the blender is used for.
time ( seconds)= energy (joules) divided by power (watts)
48000/400= 120 seconds
power is the rate at which energy is transferred 1 watt (W) is an energy transfer of 1 joule per second
if we know both the potential difference across the component and the current flowing through it then we can calculate the power using:
power (watts)= potential difference (volts) x current (amps)
calculate the power of the resistor p.d=50v I=0.2A
power (watts)= current (amps) x potential difference (volts)
50x0.2= 10 watts
calculate the power of resistor A
current= 0.5 A
potential difference= 5v
power(watts)= current (ampheres) x voltage (volts)
0.5x5=2.5 watts
if we know the current flowing through a component and the resistance then we can use this equation to calculate power:
power (watts)= current (amps)^2 x resistance ( ohms)
calculate the power of this resistor resistance= 50 ohms current=0.4 A
power (watts)= current (amps)^2 x resistance (ohms)
0.4^2 x 50
8 watts
national grid what is it
the national grid is the electricity distribution network- its a system of transformers and high voltage cables which connect power stations to consumers.
whats the problem with the national grid
energy is always lost in the power cables due to the resistance of the wires we can reduce energy lost by building power stations near homes.
what are step up transformers
electricity passes through step up transformers which increase the voltage to reduce the size of the current to reduce the amount of energy lost in the wires
so less energy is lost in the cables when the potential difference is very high
what are step down transformers
step down transformers reduce the voltage to 230 volts
reduce voltage back to safe levels for households and buildings
definition of current
rate of flow of electric charge
potential difference definition
energy transferred per coulumb of charge
describe action and purpose of a solar panel
- heats water using radiation from the sun
- water used to heat buildings provide hot water
In the northern hemisphere, the modules should always face south for the
maximum transfer of energy.
State one other factor that would affect the amount of energy transferred during
daylight hours.
angle of tilt of the cells
The temperature of the air inside the freezer compartment is –5 °C.
The air inside the fridge forms a convection current when the fridge door is closed.
Explain why.
air at the top is cold
particles are moving slowly they come together or are closer together so density increases, air is more dense
so cold air falls
and warm air rises from the bottom
Give one advantage and one disadvantage of replacing an old fridge with a new fridge
advantage- new fridge is more efficient, wastes less energy
disadvantage- it may be difficult to dispose the old fridge
when is work done
when a charge flows in a circuit
what are convection currents
currents of moving liquids transferring energy
static electricity using the concept of electric fields explain how a build up of static electricity can cause a spark
sparks are caused when high potential difference between charged object and the earth or earthed object. a high potential difference causes a strong electric field between charged object and earthed object
a strong electric field causes electrons from air particles to be removed (ionisation)
air is normally an insulator but when it is ionised it is much more conductive so a current flows through it. this is the spark.
jake removes his jumper in a dark room, as he does so he hears a crackling noise and sees tiny sparks of light between his jumper and his shirt. explain the cause of this
as the jumper rubs against the shirt, a static charge builds up on both the jumper and the shirt, this is due to electrons being removed from one and depositied on another. charge becomes large enough for electrons to jump across a small gap between the jumper and his shirt, causing a spark
explain why national grid is efficient at transferring energy refer to potential difference and current during transmission
the national grid is efficient at transferring energy because it has a step up and step down transformer. the step up transformer increases the potential difference and reduces the size of the current so that less energy is lost in the wires due to resistance so less energy is transferred to the thermal energy store of the surroundings. the step down transformer, decreases the potential difference back to save levels for households and buildings.
why does the national grid distribute electricity at a high p,d and a low current
because a high potential difference means more power distributed per second.
power is the rate at which energy is transferred so a higher power means more energy is transferred.
when is work done in appliances
work is done when a charge flows in a circuit
