P3.2 Flashcards
what is a fuse
a safety device which breaks the circuit if the current is too high
what does a fuse contain and how does it work?
a fuse contains a thin wire which melts if the current is too high
what is the rule of fuses?
work out the current and choose the next fuse up
what is the total potential difference when two or more cells are connected in series?
the sum of the potential differences
what is the total voltage when an identical cells is placed in parallel with the original cell?
the voltage stays the same
what is the equation for energy?
energy = charge x voltage
series circuit
when all components in a circuit are connected to each other in one loop
how is an ammeter connected in a circuit?
in series
what is the current in a series circuit?
the same everywhere
how is a voltmeter connected in a circuit?
in parallel
what is potential difference in a series circuit?
shared equally between components
parallel circuit
has components connected in more than one loop
what is current in a parallel circuit?
it’s shared between loops
what is potential difference in a parallel circuit?
the same everywhere
what is the equation for voltage?
voltage = current x resistance
what is resistance measured in?
Ohms Ω
what is the total resistance in a parallel circuit?
always smaller than the smallest resistance in the circuit
How does resistance change?
-sometimes you can vary the resistance of an object, like a variable resistor
-the resistance of other objects can vary as current passing through it increases
-the resistance of other objects like fixed resistors never changes
what are the expected results for a voltage - current graph for a filament bulb?
The filament wire is heated up by the current. As the wire heats up the positive ions in the wire vibrate more, making it harder for electrons to get through and therefore increasing the resistance
what are the expected results for a voltage - current graph for a diode?
Where the current is zero the resistance is very high. When the p.d. reaches a certain level in the forward direction the resistance reduces.
what are the three equations for power?
- power = energy / time
- power = voltage x current
- power = resistance x current ^2
describe the current - voltage graph for LDR
As light intensity increase more electrons are released from the semi conductor and the resistance decreases.
describe the current - voltage graph for thermistor
As the temperature increases, more electrons have enough energy to escape from the semi conductor atoms and a resistance decreases
how can the total resistance of resistors in series be found?
adding the values of the individual resistors together
