Electricity-P2 Flashcards
Equation for charge flow
Charge flow= current x time
(Coulombs). (Amps). (Seconds)
Q= I T
Equation for potential difference
Potential difference= current x resistance
(Volts). (Amps). (Ohms)
V = I R
Equation for total resistance
Total resistance= resistance of component 1 + resistance of component 2
(Ohms)
Rt=R1 +R2
Equation for power 1
power = current × potential difference
(Watts). (Amps). (Volts)
P = IV
equation for power 2
power = (current) ^2× resistance
(Watts). (Amps). (Ohms)
P=I^2 V
Power for energy transferred 1
energy transferred = power × time
(Joules). (Watts). (Seconds)
E=pt
Equation for energy transferred 2
energy transferred = charge flow x
potential difference
(Joules). (Coulombs). (Volts)
E=QV
What is current?
It is the rate of flow of electric charge
Why are metals good conductors?
Because they have free moving electrons
(Delocalised)
When is voltage is applied what end do the electrons move to?
It goes from negative to positive
CHARGE MOVES FROM POSITIVE TO NEGATIVE
What is the main difference between conductors and insulators?
Insulators have less free electrons
What is potential difference?
Another name for voltage difference in work done (energy transferred) by or on charge between two points in a circuit
How is an ammeter connected in a circuit?
In series (within the loop)
How is a voltmeter connected in a circuit?
Parallel to the component being measured
How can there be a potential difference, but not a current?
Incomplete circuit
What is resistance?
Opposing the flow of charge (current)
What causes resistance in a wire
Resistance is caused by the electrons colliding with the positive metal ions of the wire
Factors that affect the resistance of a wire
Length of wire
Temperature
Thickness of wire
Material of wire
What is the job of a variable resistor?
Alter the resistance of the circuit and therefore current and potential difference across different components
What is the relationship between potential difference and current for fixed resistance
Has the potential difference increases the current also increases?
What is the relationship between resistance and current for fix potential difference?
As the resistance increases the current decreases
State ohms law
Potential difference is directly proportional to the current for fix resistor resistor at constant temperature
What is meant by directly proportional?
This is a Y equals, MX graph (straight line thru origin) oh, when one factor doubles, the other factor also doubles
Describe the difference between a linear and a nonlinear graph
Linear graph- straight line
Nonlinear graph -not a straight line (curves)
Which of the live feed graph is linear
Fixed resistor, resistor at constant temperature
Which of the IV graphs or nonlinear?
Filament lamp (bulb) and diode
Explain the shape of the fixed resistor line
Resistance is Constant a straight line and follows ohms law
Explain the shape of the filament lamp, graph
As potential difference and current increases bulb gets hotter and this increases resistance
Explain the shape of the Diode graph
I’m very high resistance in reverse direction, so no current, very low resistance and forward direction so rapid increase in current
What is power?
Power is the rate of energy transfer or how much energy is transferred in one second or power equals energy divided by time
What colour is the Earth wire, and what
does it do?
Yellow/green
Prevents danger from short-circuits
What colour is the neutral wire and what does it do?
Carries the current away from the plug
BLUE
What colour is the live wire and what does it do you? (230V)
Brown
Carries current to plug
What does a fuse do?
Melts if current, it’s too high
What is a cable grip
Prevent a loose wire if cable is pulled
What is a double insulated cable
Prevents electric shock
What is alternating current? (AC) (Mains)
Changes direction of current. 50 times a second (50 Hz) found in the mains
What is direct current? (DC) (batteries)
Current that only travels in One Direction. Found in batteries.
Parallel circuits
The current splits at the junction
The voltage is not shared (same across every comp)
Multiple routes
The total current through the whole circuit is the sum of the current thru the separate components on each loop
Series circuit
The current does not split, and is the same everywhere
The voltage is shared
The total resistance of two components is the sum of the resistance of each component
Why does a bulb light up?
When the switch is closed, the circuit is complete, meaning that the current can be pushed around by the battery, leading to an energy transfer in the bulb causing it to light up
REQUIRED PRACTICAL- LENGTH OF WIRE METHOD (RESISTANCE)
- set up the circuit as shown (connect ruler with wire parallel to voltmeter
- attached is the end of the wire with crocodile clips to a meter ruler with wire filament.
- At a certain distance between crocodile clips, measures the voltage and cutrent using voltmeter and ammeter
- Use the equation or equals V over. I calculate resistance across the wire plot, a graph of resistance against length of wire to see relationship between the variables.
- repeat the steps using different lengths of the ruler.
- Errors- 0 rror crocodile clip, not at zero (systematic error
Energy lost vis heat
What is an ohmic conductor?
Conductor that follows, ohms law current is proportional to voltage v=IR
REQUIRED PRACTICAL- VI characteristics
- Set up equipment is Shown
- Use voltmeter to read the PD across the resistor.
- Use ammeter to read the current.
- Record a wide range of values in table.
- Adjust variable resistor to get different data.
- Switch direction of the battery to reverse polarity
- Values on now negative.
- Repeat all the steps for negative values.
- Draw a graph with four columns I and V should be directly proportional.
REQUIRED PRACTICAL- how the current in resistor at constant temperature varied the potential difference across the resistor
- Set up the equipment as shown
- Measure the potential difference across the resistor using voltmeter
- Record once you have obtained a wide range of results and table.
- Measure the current across the resistor at constant temperature, using the ammeter.
- Record when you have a twin, the wide range of results on the table.
- Increase the resistance by adjusting the variable resistor reverse the current by switching battery.
- Draw a graph to display the results to see if the resistor is an ohmic conductor.
(Follows, ohms law) V equals, I R
WHAT IS DIRECT POTENTIAL DIFFERNECE
Direct potential difference will produce a direct current (DC OCCURRING IN WHICH THE CHARGE CARRIERS MOVE IN ONE DIRECTION ONLY) BATTERIES ARE DC
A DIRECT PD DOES NOT GO BELOW 0v
WHAT IS ALTERNATING POTENTIAL DIFFERNCE
An alternating potential difference will produce an alternating current (AC OCCURRING IN WHICH THE CHARGE CARRIERS MOVE, BACKWARDS AND FORWARDS) MAINS ELECTRICITY IS AC
An alternating PD goes below 0 V
What is the voltage and frequency of the UK mains electricity
230V and 50Hz
WHAT ARE STEP UP TRANSFORMERS USED FOR
Step up transformers are used to increase the potential difference from the power station to the transmission cable
What are step down transformers used for
Step down transformers are used to decrease to a much lower value. The potential difference of domestic use in Homes
EXPLAIN THE NATIONAL GRID
The national grid is a group of transformers, pylons and cables, which connect power stations to towns. The electricity generated and power stations need to be transferred by the national grid. As many power stations are located in Rurel areas. Transformers increase deficiency of energy transfer that increasing and decreasing the potential difference. Work is done when current is transferred and energy is transferred as heat which reduces the power transferred in order to prevent this week and increase the voltage and decrease the current as p equals v I . The step up transformer increase the voltage to be transmitted through the cable to. They don’t heat up and saw power is in lost to step down transformer decreases the voltage to 230 V easy to be using households.
