electricity

Question 1

current

Answer 1

• flow of charge of electrons around a circuit
• unit = coulomb- when 1 coulomb of charge flows past a point in a circuit each second the current is one ampere
• to work out the amount of charge that flows in a time use Q= It / charge= current * time

Question 2

voltage

Answer 2

• voltage = amount of energy each coulomb of charge is given
• we can model a circuit as a ball(electron) being pushed up a hill(potential diference) by the cell
• the higher the hill the more energy the ball gains
• 1 volt = 1 joule per coulmob- V= W/Q or voltage = energy / charge

Question 3

resistance

Answer 3

• when electrons move around a circuit they bump into atoms in the wire. this is called resistance
• a large resistance means a small current is allowed through
• a small resistance means a large current is allowed through
• R= V/I or resistance = voltage / current
• V= IR and I = V/R

Question 4

electrical power

Answer 4

• a 100 w bulb converts 100 j of energy into heat and light every second
• power = work done (j)/ Time taken (s)
• 1 watt = 1 joule per second
• V= W/Q or V= W/It
• power = current * voltage

Question 5

fuses

Answer 5

• fuses prevent a large current passing through an appliance which might lead it to catch fire
• fuses do not protect you from an electric shock if the device is faulty- commonly used fuses are 3A, 5A and 13 A
• the fuse contains a piece of wire inside a small cartridge. the wire melts if the current is too large
• the fuse is connected to the live wire
• an alternative to fuses are circuit breakers

Question 6

which fuse should you use for a 1000w iron?

Answer 6

P= IV so I=P/V= 1000 W / 230 V ( always 230 V at home)= 4.3A always choose the next size up

Question 7

wiring a three pin plug

Answer 7

live =brown
earth = green/ yellow
neutral = blue

Question 8

paying for electricity

Answer 8

• the electricity company needs to know how much electrical energy we have used
  energy = power * time
  so they use kilowatt hours (kwh)1kwh = 1kw * 1 hour1
  kwh is called a unit and costs about 15p in 2015

Question 9

how much does it cost to run a 100 w bulb for one hour?

Answer 9

0.1 kw * 1 hour = 0.1 kwh
0.1 * 15p = 1.5 p
cost = power * time * cost per unit

Question 10

alternating and direct current

Answer 10

• direct current = the direction of the current is always the same
• alternating current = the direction of the current changes
• alternating current is the only supply where you can change the voltage with a transformer

Question 11

electricty

Answer 11

• conventional current flows from positive to negative - red terminal is positive- black terminal is negative