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
What does a thermistor do
A temp dependent resistor, resistance drops in hot conditions and increases in cool conditions - temp detectors e.g. thermostat
Steps for investigating the relationship between current, p.d. And resistance for different components e.g. filament bulb and fixed resistor
1) connect circuit. Thr component and ammeter are in series, so can be put in any order in the main circuit(voltmeter must be in parallel around the component under test)
2) change resistance of variable resistor. Measure current thru and p.d across the component
3) take several pairs of readings from the ammeter and voltmeter at a number of different resistances
4) plot the current against p.d to get I-V graphs
5) u can use this data to work out the resistance for each measurement of I and V
6) make sure the circuit doesn’t get too hot over course of experiment as it will mess up results. Do repeats and calculate means
What is current
The rate of flow of charge
What is power
The energy transferred by a device per second (W)
What are the advantages of the heating effect of an electric current
It’s good if u want to heat something e.g. a toaster, filament bulbs, electric heaters
What are the disadvantages of the heating effect of an electric current
If the temp gets too high the components in the circuit may melt and the circuit will stop working or not work properly, it also reduced the efficiency
How do low resistance wires reduce unwanted energy transfer
They reduce the energy dissipated to thermal stored as the current flows between components
How does the design and use of circuits explore the variation of resistance in a filament lamp
How does the design and use of circuits explore the variation of resistance in a diode
How does the design and use of circuits explore the variation of resistance in a thermistor
How does the design and use of circuits explore the variation of resistance in a LDR
How does the current vary with potential different for a filament lamp
How does the current vary with potential different for a diode
How does the current vary with potential different for a fixed resistor
What is the design and construction of series circuits for testing and measuring
What does power transferred by a device depend on
The p.d across it and the current flowing thru it
