Electricity Flashcards
(39 cards)
Tell me about a series circuit
- same current through each component
- potential difference is shared between components
- total resistance is the sum of the resistance of each component
Tell me about a parallel circuit
- same potential difference across each component
- current is shared so total current is the sum of the currents through each component
- total resistance is less than the resistance of the smallest of the two resistors
so adding a resistor reduces the total resistance
Why does adding resistors in a series increase the total resistance?
Because the current must flow through each resistor sequentially, experiencing the resistance of each in turn, effectively adding up the individual resistances
Why does adding resistors in parallel decrease the total resistance?
There are multiple paths for current to flow
What is current?
The rate of flow of charge
At a constant temperature, what is the relationship between the current and potential difference? Ohm’s law
The current flowing through an ohmic conductor is directly proportional to the potential difference across it
What factors affect the resistance of a piece of wire
- Temperature ->increased temp = increased resistance
- Length -> increased wire length = increased resistance
- Cross sectional area -> increased area = decreased resistance
- Material
How do we describe the relationship between resistance and length?
Resistance is directly proportional to length
As length doubles, resistance doubles
A straight line through the origin
How do you investigate factors affecting resistance?
- Attach a crocodile clip to the wire level with 0cm on the ruler
- Attach the second crocodile clip to the wire e.g 10cm away and write down the length of the wire
- Close the switch then record the current through the wire and the pd across it
- Open the switch then move the second crocodile clip
- Repeat for a number of different lengths
Tell me about the resistance of a lamp
As the resistance of a lamp increases, the temperature of the lamp increases, increasing the current.
The increasing current eventually increases the resistance, which means less current can flow per unit so the graph gets shallower - hence the curve
Tell me about the resistance of diodes
Current will only flow through a diode in one direction. The diode has a very high resistance in the reverse direction
What happens to the resistance of a thermistor as the temperature increases?
the resistance of the thermistor decreases
What happens to the resistance of a LDR as the light intensity increases?
the resistance of the LDR decreases
Bright light - decreases
Dark - increases
What kind of supply is main electricity?
AC supply
What is the frequency and potential difference of the domestic electricity supply in UK
50Hz, 230V
What is the difference between direct and alternating current
AC - the current is constantly changing direction so alternating voltages
DC - current is always flowing in the same direction so direct voltage where the positive and negative ends of the source are fixed
What does the live wire do and what colour is it?
Brown - carries the alternating potential difference from the supply (230V)
What does the neutral wire do and what colour is it?
Blue - completes the circuit and carries away current - electricity normally flows in through the live wire and out through the neutral wire. It is at 0V.
What does the Earth wire do and what colour is it?
Yellow and green - stops the appliance casing from becoming live, it doesn’t carry a current - only when there’s a fault. 0V
Why can the live wire give you an electric shock?
Your body is at 0V. If you touch the live wore, a large potential difference is produced across your body and a current flows through you.
Even if a plug is off, there is still pd in the live wire so if you made contact your body would provide a link between the supply and the earth, so a current would flow through you
Why is it dangerous if the live wire and earth wire touch?
If the link creates a low resistance path to the earth, a huge current will flow, which could result in a fire
What does the amount of energy can appliance transfers depend on?
How long the appliance is switched on for and the power of the appliance
How do kettles transfer energy?
electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle
How do fan’s motor transfer energy
electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor
