Paper 1 Electricity Flashcards
A direct current flows in how many directions?
A direct current flows in ONE direction only
eg car batteries, solar cells
On a Voltage-time graph is would appear as a STRAIGHT HORIZONTAL line
What direction does an ALTERNATING CURRENT flow>
An ALTERNATING CURRENT regularly CHANGES direction
On a Voltage-time graph is would appear as a CURVE alternating between + and - line
Eg
What wires are good conductors?
Copper wires are good conductors
What is a good insulator?
Plastic is a good insulator
BROWN wire
. LIVE - to right
. Carries 230V
. Brown wire
Blue wire
. NEUTRAL wire
. Blue wire
. It completes the circuit at 0v
Yellow & Green
. Yellow & Green is earth wire
. O v
. There for safety
. Does not form part of the normal circuit
What could happen if no earth wire?
Without an earth wire … ELECTROCUTED
ENERGY =
ENERGY = P x t (J) = (W) (s)
POWER =
POWER = V x I (W) = (potential difference) x (current in Amps)
What is the MAINS VOLTAGE in this country?
. The MAINS VOLTAGE in this country voltage in this
country is 230 V.
. The current ALTERNATES will a FREQUENCY of 50 hertz (Hz)
. ac supply (alternating current
Which wire does the fuse connect to?
The fuse connects to the LIVE wire
What power is transmitted by a 5 A current through a 10 Ω resistor?
250 W is the power transmitted. P = I²R, P = 25 × 10 = 250 W. Don’t forget to square the current.
What is a step down transformer?
A step down transformer…
A step down transformer INCREASES the current and LOWERS the voltage.
Electrical appliances - type of energy
Electrical appliances - type of energy
. CHEMICAL (from power stations)
. KINETIC - to start the fan or oven
energy = power × time
Energy = POWER x TIME
(s)
P = V x I
P = V x I
Power (P) is measured in watts (W)
potential difference (V) is measured in volts (V)
current (I) is measured in amps (A)
What are TRANSFORMERS used for?
Transformers are used to CHANGE VOLTAGES & CURRENTS in transmission lines.
How can the power transferred be kept the same?
As the power transferred must stay the same:
. increasing voltage decreases current
. decreasing voltage increases current
Transmission through thick cables held up by pylons
power = current2 × resistance
P - I2 x R
power (P) is measured in watts (W)
current (I) is measured in amps (A)
resistance (R) is measured in ohms (Ω)
Electric current created chemically is always …
Electric current created chemically is always DIRECT.
Alternating current is generated using …
Alternating current is generated using MAGNETS
The earth wire provides …..
The earth wire provides a LOW RESISTANCE path to ground. A high resistance path would not cause the fuse to melt.
Power =
Power = E/t
Efficiency =
useful energy transfer/total energy transfer
or Efficiency =
useful power output/total power input
An efficiency of 0.5 or 50% means …
50% efficiency = half the energy is useful but half is wasted.
Neutral/blue wire does what?
Neutral wire carried the current away from the appliance.
Definition of National Grid
Links power to homes and business by cables and transformers transferring Electrical Power
Power Station
Transfers the energy supply into electrical energy 25,000V
Step up transformer
Step up transformers INCREASE the VOLTAGE from the POWER STATION to the TRANSMISSION CABLES
Transmission cables
Transmission cables - TRANSFER the electricity
Step down transformers
Step down transformers - reduce the voltage from the TRANSMISSION CABLES for DOMESTIC USE (houses & shops) to 230V
