18 Flashcards
For current to flow
- Needs a complete circuit
- something to push it around the circuit (by cell, battery or power supply)
Good conductors
Most metals: copper, silver, gold and water
Bad conductors
Good insulators: polymers such as Perspex or poly theme, wood and glass
What is a electric current
- a flow of electrical charge
- in a metal, current is a flow of electrons
- Si unit - ampere
- 1milliamp =10^-3
- 1microamp = 10^-6
Ammeter - measures electrical current
Why are things good conductors
Because they contain electrons that can move about freely within material
- a voltage is provided by a battery or power supply
- a voltage can start these conducting electrons moving in one direction through a he metal
Electrons
A negative electric charge -> attracted to the positive terminal of the battery
Conventional current
Flows (a flow of positive flow) moving + to -
Electron flow
Electron flow ( a movement of conducting electrons) from - to +
Current: symbol, unit and symbols for unit
I - quantity symbol
Amps - unit
A - symbol for unit
Charge: symbol, unit and symbols for unit
Q-symbol for quantity
Coulombs - unit
C - symbol for unit
Time: symbol, unit and symbols for unit
t - symbol for quantity
Seconds - unit
s - symbol for unit
Meaning of current
The rate at which electric charge passes a point in a circuit
Trip switches
Power supplies are protected by trip switches to cut out if to large current flow
The current following
Controlled by the electrical resistance to the circuit
Measured in ohms
Resistance = p.s (v) / current (A)
R = V/I
Changing current
The greater the resistance => the smaller the current
The greater the p.d => the greater the current that flows
Through think and thin wire
Longer the wire, greater resistance
Smaller the diameter of wire => greater the R
Potential difference
Is and the term for voltage as it is measured in volts(V) using a Voltmeter
Special name for p.d across a cell = e.m.f also measured in volts
E.m.f = electro motive force
Any component that pushes current around a circuit is said to have an e.m.f
E.m.f
P.d at the terminals when there is no current flowing, it is a voltages produced by a power source.
Energy transferred per coulomb/unit charge
Equation for power
P= IV
Unit W
P= E/T
Energy transformed/ time taken
Resistance equation
R=V/I
Unit Ohums
Energy equation
E= IVT
(T = must always be in seconds)
Unit J
Charge, current and time equation
Charge = I/T Current = C/T
*triangle.
