P4 - Electric Circuits Flashcards
What is current?
The flow of electrical charge
What is the unit for current?
Amperes (A)
What conditions are compulsory for electrical charge to flow around a circuit?
The circuit needs to be complete
There is a source of potential difference
What is potential difference?
The driving force that pushed the charge around the circuit
What is potential difference measured in?
Volts (V)
What is Resistance?
Anything that slows the flow in the current down
What is the unit for resistance?
Ohms
What is the relationship between resistance and current in a circuit?
The greater the resistance across a component, the smaller the current that flows
What is Charge flow measured in?
Coulombs (C)
What is the equation that links charge flow, current and time?
Charge flow = current x time
What is the formula linking potential difference and current? (Ohms law)
V = IR
What does the ammeter measure and what does the voltmeter measure?
Current (amps)
Potential difference (volts)
If the resistance is kept constant and the potential difference is increased, what will haooen to the current?
It should increase proportionally
What happens when you increase the temperature of a circuit?
The resistance will increase
What are diodes?
Devices that only allow current to flow in one direction
What does LDR stand for?
Light Dependent Resistor
What is a LDR (light dependent resistor?
A resistor with resistance that depends on light intensity
What is a thermistor?
A temperature dependent resistor
What happens to the resistance of an LDR in Bright light and darkness?
Bright light - resistance is low
Darkness - resistance is high
What happens to the resistance in a thermistor in hot and cool conditions?
Hot - the resistance drops
Cool - the resistance increases
What is the main difference between a series and a parallel circuit
A series circuit has only one single loop while a parallel circuit has more than 1 loop
Why are parallel circuits generally more reliable than series circuits?
If any loop in a parallel circuit breaks, the circuit can still flow
How do you carry out the resistance practical?
- Attach a wire to a meter ruler using tape and connect the wire to the circuit using crocodile clips
- Move the crocodile clips to the 30cm mark
- Record the voltage of the battery/cell and use the ammeter to find the current.
- Find the resistance using V=IR
- Repeat this, moving the crocodile clip up in 10cm until you get to 100cm
- Plot the data on a graph
What is the ‘National Grid’?
The giant network of transformers and wires that spreads across the country to distribute electricty
Where does most of the UKs electricity come from?
Power stations
How do power stations generate electricity?
Fuel is burned to heat water to produce steam
This steam spins the turbine
The turbine drives a generator which produces electricity
What is the equation that links power, voltage and current?
P = V x I
Why does a high current generate lots of heat?
Due to the resistance
The resistance slows down the flow of electrons, and the energy lost in the process is released as heat
Why is a high current bad when trying to transfer electricty?
Loses energy to thermal energy
How do you make a circuit have a low current?
Increase the voltage
What are step up transformers?
A device that increases the voltage in a circuit
Why is a Step up transformer used in the National Grid?
It increases the voltage and decreases the current
This is to minimise thermal energy energy loss to the surrounding
This increases efficiency for Electrical power transmission
What does ‘direct potential difference’ mean?
Potential difference in one direction only
Why are Step Down transformers used in the National Grid?
It decreases the dangerously high voltage to a safer and more usable value (230V)
