P2.3 - Currents in electrical circuits Flashcards
When certain insulating materials are rubbed together they become…
…electrically charged
How do these materials become electrically charged?
Negatively charged electrons are rubbed off one material and onto another
What charge does the material that gains electrons have?
Negative
What charge does the material the loses electrons have?
Positive
What happens when two electrically charged materials are brought together?
They exert a force on each other
Two objects that carry the same types of charge…
…repel
Two objects that carry different types of charge…
…attract
Can electrical charges pass more easily through some substances?
Yes, such as metals
What is electric current?
A flow of electric charge
What is the size of the electric current?
The rate of flow of electric charge
What is charge measured in?
Coulombs (C)
What is current measured in?
Amps (A)
What is potential difference?
Voltage
What is the potential difference between two points in an electric circuit?
The work done per coulomb of charge that passes between the points
What is the symbol for an open switch?
A broken line, with the middle third at an angle, with a circle at the joins
Why are thermistors needed in circuits?
In thermostats
What is the symbol for a cell?
2 ‘T’ shapes facing opposite ways, one with a thicker top
What is the symbol for a battery?
2 ‘T’ shapes facing opposite ways, with thin and thick lines the opposite ways round an a dotted line in between
What is the symbol for a diode?
A circle which the wire cuts through, with a triangle in it, with a vertical line on the forward facing point
What is the symbol for a resistor?
A rectangle which the wire doesn’t cut through
What is the symbol for a variable resistor?
A rectangle which the wire doesn’t cut through, with an arrow over the top
What is the symbol for a lamp?
A circle with a cross through it
What is the symbol for a fuse?
A rectangle whch the wire cuts through
What is the symbol for a voltmeter?
A circle with a capital V in it
What is the symbol for an ammeter?
A circle with a capital A in it
What is the symbol for a thermistor?
A rectangle with a line through, and a a tail parallel to the wire
What is the symbol for an LDR?
A resistor symbol in a circle with arrows pointing at it from the top left corner
What is the symbol for an LED?
A diode symbol with arrows pointing away from it in the top right corner
Why are LDRs needed in circuits?
For switching on lights when it gets dark
What are current-potential difference graphs used to show?
How the current through a component varies with the potential difference across it
What does the current-potential difference graph for a resistor at constant temperature look like?
Directly proportional
What does the current-potential difference graph for a resistor at constant temperature look like?
Directly proportional
How can the resistance of a component be found?
By measuring the current through, and potential difference across the component
The current through a resistor is directly proportional to…
…the potential difference across the resistor
What is resistance measured in?
Ohms
What does the current through a component depend on>
Its resistance
The greater the resistance…
…the smaller the current for a given potential difference across the component
The potential difference provided by cells connected in series is the sum of…
…the potential difference of each cell
In series circuits…
- the total resistance is the sum of the resistance of each component
- there is the same current through each component
- the total potential difference of the supply is shared between the components
In parallel circuits…
- the potential difference across each component is the same
- the total current through the whole circuit is the sum of currents through the separate components
