Current + Voltage In Circuits Flashcards
What is the flow of charge called
Electric current
Insulators
All electrons are held tightly in position, unable to move from atom to atom
Charges unable to move through insulators
What does an ammeter measure
Current
I in amps
What is electric charge measured in
Coulombs
Charge equation
Charge (Coulombs) = current x time
What does a voltmeter measure
Voltage in volts
Energy transferred equation
Energy transferred (joules) = charge x voltage
‘Single loop’ circuit
Series circuit
More than one path circuit
Parallel circuit
In a series circuit…..
- current same
- voltage splits
In a parallel circuit
- current splits
- voltage same
What does Ohm’s law state ?
The resistance of a component is given by voltage/current and for a resistor is constant at a constant temp
For a given resistor….
More voltage gives more current
For a given voltage……
A larger resistance has a smaller current
Resistance equation
Resistance = voltage/current
Resistance = in ohms
For a fixed resistance…..
Current is proportional to voltage
For a metal filament lamp…..
Resistance increases when current increases
For a diode…..
In reverse direction (infinite resistance and no current)
In forward direction (small resistance)
Resistance of a thermistor
The resistance of the thermistor decreases if the temp increases
Experiment for thermistor:
1) measure initial temp of the water (thermometer), record one voltage a current
2) repeat this changing the temp of the water each time, record voltage and current each time
3) using the equation voltage/current, work out resistance
4) plot a graph of resistance against temp
Experiment for light dependant resistor (LDR):
1) use a ‘light meter’ to measure light intensity
2) vary the distance the bulb is from the LDR, or vary the brightness of the bulb
As light intensity increases…..
Resistance decreases (non linear)
What do LDR and thermistor act as?
Sensors, they respond (automatically) to an external property
How to answers question about LDR or thermistor?
1) pick a change
2) say how the resistance of the device changes
3) say how the current through the circuit changes
4) say what happens to the output device
5) give a practical use of the circuit
Thermistor example answer
As temp rises, resistance of thermistor falls, Current in circuit rises, Bulb comes on
Use: alert to show when a temp of a soldering iron is too hot
Use of an LDR
Alarm to show when a light in a photographic dark room gets too bright
Current + charge equation
Current = charge flowing / time taken
Energy + voltage equation
Energy transferred = charge x voltage
Volts equation
Volts = joules / coulombs
What is a volt
1 volt = 1 joule per coulomb
What is DC
Direct current
Current that flows in one direction
What is AC
Alternating current
Current constantly changing direction
UK mains voltage and frequency?
Voltage = 230 V Frequency = 50Hz
What current does uk mains work on
AC
What is a safe voltage for uk mains?
50V
