Electricity

Created by

Arjun Cherukuri

Cards (129)

Standard electrical symbols
Function of cell/battery
Provides the cirucit with a source of potenital difference. A battery is two or more cells
Function of a switch 
Turn the circuit on (closed), or off (open)
Function of fixed resistor
A resistor limits the flow of current. A fixed resistor has a resistance it cannot chnage
Function of a variable resistor
A resistor with a slider that can be used to change its resistance. These are often used in dimmer switches and volume controls
Function of a thermistor
The resistance of thermistor depend on its temperature. As its temperature increase, it resistance decreases and vice versa
Function of light-dependent resistor (LDR) 
The resistance of an LDR depends on the light intensity. As the light intensity increase, the resistance decreases and vice versa
function of a diode
A diode allows current to flow in one direction only. They are used to convert AC to DC current
Function of ammeter
Used to measure current in a circuit. Connected in series with other components
Function of voltmeter
Used to measure the potential difference of an electrical component. Connected in parallel with the relevant component
In a circuit diagram what is the direction of current flow always from?
The positive to the negative terminal of power supply
What is the potential difference across a component in a circuit is defined as?
The energy transferred per unit charge flowing from one point to another
What is electric current?
The flow of electrical charge measured in amps
What is the size of the electric current?
The rate of flow of electric charge or a flow of electrons
In a circuit that is a closed-loop what is current?
Same value at any point - number of electrons per second that passes through one part of the circuit is the same number that passes through any other part of the
What is resistance defined as?
Opposition to current - higher resistance of a circuit - Lower the current - good conductor have a low resistance and insulators have a high resistance
What does the current through a component depend on?
the resistance of the component and the potential difference across it.
What happens to the potential difference and current when the resistance is greater?
The lower the current for a given potential difference across the component and vice versa
Required Practical: Investigating Resistance of the length of a wire at a constant temperature variables
Independent- length of resistance wire
Dependent - resistance
Control variable - potential difference of the power supply, temp of the wire
Diagram of apparatus
Method for this practical
1. Set up the apparatus by connecting two crocodile clips to the thin resistance wire a distance of 10cm apart and setting the power supply to 1.5V
2. Connect the wire, using the clips, to the rest of the circuit
3. Record the potential difference from the voltmeter and current from the ammeter
4. Move the clips in 10cm intervals further apart
5. Take new measurements from the voltmeter and ammeter each length reading
6. Continue until the crocodile clips are a length of 1m apart
What equation would you use for this experiment
R=V/I
What is the resistance to the length of the wire
Directly proportional as the graph is a positive correlation as the longer the piece of wire, the higher the resistance
Combination of resistors in series and parallel practical variables
Independent - number of resistors
Dependent - total resistance
Control - Potential difference of power supply, temp of the resistors
Diagram of this method parallel
Diagram of this method parallel
Method for this practical
1. Connect the circuit shown in figure 1 with a battery of 4V, first with one resistor with the voltmeter connected in parallel and ammeter in series
2. Close the switch and record the reading on the voltmeter and ammeter
3. Repeat steps 1 and 2 for just the second resistor
4. Open the switch and connect both R1 and R2 in the series as shown in figure 2, connecting the voltmeter in parallel to both resistors
5. Close the switch and record the new readings on the voltmeter and ammeter
6. Open the switch and arrange R1 and R2 now in parallel shown in figure 3
7. Close the swich and record the readings on the voltmeter and ammeter
What should the results show in series?
The resistance of the combined resistors is equal to the sum of the two individual resistances - because the electrons flow through just one path through both resistors, so the current does too
What should the results show in parallel?
The resistance of the combined resistors is less than the sum of three two individual resistances - this is because the electrons are split between the different paths or loops but the resistors still have the same potential difference across them
Systematic errors for both experiments
First crocodile clip must start at 0 on the ruler - could cause a zero error
Both the ammeter and voltmeter should be checked to start from 0
What does Ohms law state?
The current through a conductor is directly proportional to the potential difference across it
What are referred as ohmic conductors?
Electrical conductors that obey Ohm's law
Examples of ohmic conductors
Fixed resistors, wires and heating elements
When is ohms law only relevant?
At constant temperatures
Is a filament lamp an ohmic conductor?
No
Why is the current and potential difference not directly proportional in a filament lamp?
The resistance of the filament lamp increases as the temp of filament increases
I-V graph for filament lamp
Why is an increase in temp causes an increase in resistance?
The higher the temp, the faster these atoms vibrate -
The electrons collide with vibrating atoms which impedes their flow hence the current decreases
If the current decreases, then the resistance will increase
Increase in temp cause an increase in resistance
Is a diode a non-ohmic conductor?
Yes
What does it only allow?
Current to flow in one direction only which is called forward bias