(Done) Electricity (Paper 1) Flashcards
Define electrical current
- Electrical current is the flow of electrical charge
What circumstances are required for electrical charge to flow (2)
- The circuit is complete
- There is a potential difference
Calculation relating Charge, Current and time
- Charge (Q) = Current (I) / Time (t)
Calculation relating Potential Difference, Current and Resistance
- Potential difference (V) = Current (I) x Resistance (Ω)
Define an Ohmic conductor and its features
- Something where the resistance doesn’t change with current
- At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the PD across it
Features of an LDR
- Resistor dependent on the intensity of light
- Bright light, low resistance
- Darkness , high resistance
- Used in automatic night lights
Features of Therimistors
- Temperature dependant resistor
- High temperature, low resistance
- Low temperature, high resistance
- Used in thermostats
What are sensing circuits used for
- To turn on or increase the power to components depending on the conditions they are in
Define series circuits
- The different components are connected in a line, end to end, between the +ve and -ve of the power supply
Features of a series circuit (4)
- Potential difference of the power supply is shared between all components
- Current is the same everywhere
- The total resistance of two components is the sum of their resistances
- Cell potential difference adds up
Define parallel circuits
- Each component is separately connected to the +ve and -ve of the supply
Features of parallel circuits
- Potential difference same across all components
- Current is shared between all branches
- if you add a resistor in parallel, the resistance is less than the smallest resistor
Types of electrical supplies (2)
- Alternating current
- Direct current
How are alternating currents produced
- When the voltage of the current is constantly alternating between positive and negative
Features of the UK mains supply
- A 230 V alternating current
What type of current do cells and batteries provide
- Direct current
Features of the Live wire in a plug
- Brown
- Provides the 230v alternating potential difference from the mains
Features of the neutral wire
- Blue
- Completes the circuit for current to flow
- It is around 0V
Features of the earth wire
- Green and yellow
- Prevents the appliance casing from becoming live
- It is also 0V
Why can you get an electric shock from a live wire
- Your body has 0V
- If you touch the live wire, there is a potential difference between you of 230V
Calculation relating energy transferred, Power and time
- Energy transferred (J) = Power (W) x Time (s)
What does the power rating on an appliance tell you
- The maximum amount of energy transferred between stores per second when the appliance is in use
Calculation relating energy transferred, charge flow and potential difference
- Energy transferred (J) = Charge flow (C) x Potential difference (V)
Calculation relating power, potential difference and current
- Power (W) = Potential difference (V) x Current (A)
Calculation relating power, current and resistance
- Power (W) = Current^2 (A) x Resistance (Ω)
Define national grid
- Giant system of cables and transformers that covers the UK and connects power stations to consumers
How does the national grid cope with changes in demand
- Running well below maximum output so there is spare capacity to cope with high demand
- Lots of smaller power stations that can start up quickly
Why does the national grid have high potential difference and low current
- To transmit huge amounts of power you need either a high current or high Pd
- A high current causes large amounts of waste energy as the wires heat up
What is the relationship between potential difference and current at a constant power
- as the Pd increases, the current decreases and vice versus
What is used to increase and decrease potential difference in the national grid
- Step-up and step-down transformers
How do transformers work
- Transformers all have two coils, primary and secondary, joined with an iron core.
- To increase, you must have more turns on the secondary than the primary coil
- To decrease you must have more turns on the primary than the secondary coil
Calculation relating pd and current in primary and secondary coils
- Pd across secondary coil (V) x Current in secondary coil (A) = Pd across primary coil (V) x Current in primary coil (A)
How does friction cause a build up of static electricity
- When certain insulating materials are rubbed together, negatively charged electrons will be scraped off of one and dumped onto another
- This will leave the materials electrically charged with an equal positive and negative charge accordingly
How does a build up of static electric charge cause sparks
- As electrical charge on an object increases, the Pd between the object and the earth increases
- If the Pd is large enough, electrons can jump across the gap between the charged object and the earth (or any earthed conductor)
When does an electric field appear
- Around any charged object
How do electric fields cause sparks
- High Pd causes a strong electric field
- Strong electric field causes electrons in air particles to be removed (ionised)
- This causes the air to be able to have current flow through it
