P2 Electricity Flashcards
What is current?
Flow of electrical charge
What needs to be present for electrical charge to flow around a complete circuit?
Potential difference
Unit of current
Ampere
What needs to be true if the current has the same value everywhere?
A single, closed loop
What is volatge
The driving force (potential difference) that pushes the charge around (volts)
Resistance
Everything that slows down the flow
What factors affect the current?
Potential difference and resistance
What is the size of the current?
The rate of flow of charge (more charge passes around the circuit when a larger current flows)
Potential difference forumla
V = A * R
Ammeter
- Measures the current in amp
- Must always be placed in series with whatever you’re investigating
Voltmeter
- Measures the voltage across the test wire
- Must always be placed parallel around whatever you’re investigating
Ohmic conductors resistance does not change with (at a constant temperature) …
current
When the heat increases, the resistance and current …?
Increases
Diodes resistance
- Allow current flow in one direction
- Doesn’t allow current flow in the opposite direction
LDR
- Resistor that is dependent on the intensity of light
- Indirectly proportional
Thermistor
- A temperature dependent resistor
- Indirectly proportional
Why can LDR’s and thermistors be important?
- They can be used to turn on certain circuits
- Conditional dependant
Energy transferred depends on?
Power
What determines the power of an electrical appliance?
How much energy it transferes per second
Energy transferred by electrical work equation
Energy = Power * Time
What is a power rating
A label with the maximum safe power that they can operate at
What are some downsides to higher power?
- They can be less efficient
- The energy won’t be put to exactly one process (could be sound, or thermal)
What is potential difference in terms of charges passed?
Energy transferred
Energy transferred J =
Charge * Potential difference
Power (W) =
Potential difference * Current
National Grid
- A giant system of cables and transformers that cover the UK and connects power stations to consumers
- Transfers electrical power from power stations anywhere on the grid to anywhere else on the grid where it’s needed
Why does the national grid use a high Pd and a low current
- A high current loses loads of energy as the wires heat up and energy is transferred to the thermal energy of the surroundings
- Much cheaper and keeps the current power low as possible
Transformer
- 2 coils joined with an iron core that increases or decreases the potential difference
- The secondary coil has more turns than the primary coil
- Therefore the current is decreased
- The transformers are practically 100% efficient
