P4 Flashcards
What is electric current
Electrical charge
A current can only flow if there’s a source of
Potential difference (electrical charge will only flow round a complete circuit if there is a potential difference)
A component
Anything you put in a circuit
Charge flow, current, time
Charge flow (coulombs C) = (current A) x time (s)
Q = I x t
An electric current of 1 A is a rate of flow charge
Of 1 C per second
Electrical charge will only flow round a complete circuit if there is a
Potential difference, so a current can only flow if there’s a source of potential difference
The unit of current is
Ampere
In a single, closed loop the current
Has the same value everywhere in the circuit
Potential difference, current, resistance
Potential difference (V) = current (A) x resistance (O with two legs)
V = I X R
Potential difference definition
The potential difference (voltage) between two points in an electric circuit is the work done (energy transferred, J) per coulomb of charge that passes between the points.
The size of a current is the
Rate of flow of charge
Ohms law states that
’ the current through a conductor is directly proportional to the voltage across two points
Resistance
Anything that slows the flow down measured in ohm
The current through an ohmic conductor is directly proportional
To potential difference so you get a straight line (see page 26 cgp to see IV graph
The greater the resustance across a component, the smaller the
Current that flows (for a given potential difference across the component
Filament lamp (I-V graph)
26 cgp. As the current increases, the temp of the filament increases, so the resistance increases. Meaning less current can flow per unit, so the graoh gets shallower
Diode (I-V graph
Current will only flow through a diode in one direction, as shown. The diode has very high resistance in the reverse direction
Diode
Only lets current flow in one direction
Thermister IV graph
A thermister is a component which changes resistance due to temperature. As temp increases, thermistors resistance decreases. Pic on slides 15 in 4.4
Light dependent resistor IV graph
An LDR is a component which changes its resistance due to intensity of light. As light intensity increases an LDR’s resistance decreases. Graph on page 16 of slides 4.4
