Electricity And Circuits Flashcards
What is the difference between a series and parallel circuit
Series:
There’s a bigger supply p.d. When more cells are in series
Current = same everywhere
Total resistance increases as you add resistors
Parallel:
P.d. = same across all components
Current = shared between branches - total current flowing around the circuit = the total of all currents thru the separate components
There are junctions where the current splits of rejoins
Total resistance decreases if u add a 2nd resistor in parallel
What does current need to flow
Current will only flow thru an electrical component if there is a p.d. Across that component and if the circuit is complete (closed)
What does current depend on
The p.d and the resistance of the component
When is the current high
When the p.d is high
When is the current low
When the resistance is high
What is current
The rate of flow of charge
What is unit of charge
Coulombs (C)
What is unit of current
Amperes (A)
What is unit of resistance
Ohms (Ω)
What is the unit for p.d.
Volts (V)
Where is current conserved
At a junction in a circuit
Why is the net resistance increased if 2 resistors are in series
The 2 resistors have to share the total p.d. so the p.d. Across each resistor is lower so current thru each is lower
The total current in the circuit is reduced when resistor is added which means the resistance increases
Why is the net resistance decreased when 2 resistors are in parallel
If u have 2 resistors in parallel their total resistance is less than the resistance of the smallest of the 2 resistors
Both have the same p.d, by adding a loop the current has more than one direction to go in, increasing the total current means a decrease in resistance
What does an ammeter do and where’s it connected
In series with a component to measure the current in the component
What is the current caused by in metals
A flow of electrons
How can changing the resistance in a circuit change the current, how can it be achieved using a variable resistor
What is the p.d.
The energy transferred per coulomb of charge that passes between 2 points in an electrical circuit
What is the p.d across an electrical component
The amount of energy transferred by that electrical component per unit charge passed
What does 1 volt equal to
One joule per coulomb
What does resistance usually increase with
Temperature
Why does resistance usually increase with temperature
When an electrical charge flows thru a component, it has to do work against resistance which causes an electrical transfer of energy, some of this energy is transferred usefully but some is dissipated to thermal energy stored of the components and surrounding - when a current flows thru a resistor it heats up
Why does a resistor heat up when current flows thru it
Because the electrons collide with the ions in the lattice that make up the resistor as they flow thru it. This gives the ions energy which causes them to vibrate and heat up
What happens to a thermistor when there’s an increase in temp
The resistance decreases
What does an LDR do
Depends on light intensity, in bring light, the resistance falls and in darkness the resistance in highest - automatic night lights, burglar detectors
