Topic P2 - Electricity Flashcards
What is a charge?
A value of electricity flowing through a circuit.
What does a closed switch do?
Allows current to flow through.
What is a cell?
A component that pushes current around the circuit.
What is a battery?
Two cells together
What does a diode do?
Only allows current to flow in one direction.
What does a LED do?
Light emits when current flows through.
What is a thermistor?
Value that changes with temperature.
What is a LDR?
The resistance changes with brightness.
What is a Ammeter?
Measures current. connected in series
What is a voltmeter?
Connected in parallel with measures Voltage.
What is a Fuse?
Set a maximum value on the current that can follow through in a circuit.
What is current?
Flow of electrical charge
What is Potential difference?
Driving force that pushes the current around.
What is Resistance?
Slows down the current
Does current flow through closed or open circuits?
closed, if there is a pD.
The greater resistance across a component means what?
The smaller the current that flows.
How do work out charge flow?
Q = I T
Q is charge flow in Coulombs
I is Current in Amps
T is time in seconds.
A current of 2A flows through a bulb for 3 minutes. Calculate the amount of charge that flows through the bulb in this time?
Q = I T
3 X 60 = 180 seconds
180 X 2 = 360C
A charge of 5kc flows through a variable resistor in 2 minutes. Calculate the reading on the Ammeter which is connected to the circuit?
I = Q/T
5 km = 5000 m
C = 5000
5000/120 = 41.7 A
What is the Equation for Potential difference?
V = I R
V equals voltage in Volts
I is amps in ampere
R is resistance is Ohms
A circuit is composed of two 1.5 V cells, an ammeter and a fixed resistor. If the ammeter reads 0.5 A calculate the resistance of the resistor.
V = 3V I = 0.5A R = V/I = 6 ohms.
I K ohms equals how many ohms?
1000 ohms
If you double the resistance what will happen to the Current?
The current will half. The current is inversely proportional to the resistance.
What equipment are you going to use when finding how length of wire affects resistance?
Battery Ammeter Voltmeter Length of wire Ruler Crocodile clips
What is the method to test how length of wire affects resistance?
1) Attach crocodile clips to the wire level with 0 cm on the ruler.
2) Attach the second crocodile clip to the wire 10 cm away from first clip write down the length. between clips.
3) Close switch and record current and Pd.
4) open switch adjust the length of wire and then close and work out resistance by using current and Pd
In this experiment the length of wire is what to the resistance?
Directly proportional.
What are the problems with the experiment in finding how the length of wire affects resistance?
There is some resistance caused by the contact between the crocodile clip and the wire.
How can you increase the resistance of the experiment finding out how length of wire affects resistance?
Using a longer wire.
What is a variable resistor?
Contains long pieces of wire in a coil, we can change the length of the wire that current runs through it.
What does the variable resistor control?
It controls the potential difference across the lamp by increasing the resistance, which can make lamp dimmer. .
Why would you want to add a resistor to a circuit?
If you want to make lamp dimmer, add an resistor, meaning less electrical energy is transferred to the lamp, so it is not as right.
If you increase the potential difference what also increases?
The current.
What is a Ohmic conductor?
The current through a resistor directly proportional to the Potential difference. This means the resistance is constant. The resistance doesn’t change if we increase current. The resistance will only stay constant, if temperature is constant.
What is the equipment needed to look at I-v Characteristics?
Variable resistor, component voltmeter Ammeter
What is the method to that looks at the I-V characteristics?
Vary the variable resistor, allowing current through the circuit and the Pd across the component.
2) Use ammeter to read the current through a resistor and Pd.
3) Adjust the variable resistor and record current and Pd
4) Switch directions of battery ( meaning pd is reversed, and the ammeter and voltmeter should be negative)
5) Repeat this with a filament lamp and a diode changing the Resistor.
For a filament lamp describe the shape?
The current is not proportional to Potential difference, this is because as current increases the temp increases, causing the resistance to increase.
For a diode describe the shape?
In a diode we only get current at 0,6-0.7 Volts. With a diode there is no current when pD is reversed because it has a high resistance in reverse.
What is a light Dependent resistor?
It is dependent on the light intensity
For a LDR what happens to resitance when Light?
The resistance falls.
For a LDR what happens to resitance when Dark?
Resistance is at its highest.
What is a thermistor?
It is a temperature dependent resistor.
In hot conditions for a Thermistor, what happens to resistance?
It drops
In cool conditions for a Thermistor, what happens to resistance?
Resistance goes up.
Name an everyday use of the component LDR?
Automatic night lights.
Name an everyday use of the component a thermistor?
Thermostats
In series current is what?
It is the same everywhere.
In parallel what happens to the current?
It is shared between branches.
What is the potential difference in a Series circuit?
Potential difference of power supply is shared between components
What is the potential difference in a Parallel circuit?
The pD is equal across each branch.
What is the total resistance in a series circuit?
sum of resistance in each component.
What is the potential difference in a Paralegal circuit?
The total resistance of the 2 resistors in parallel are less than the resistance of the smallest individual resistor.
In parralel adding a resistor does what?
It reduces the resistance
Explain what happens to the current and resistance in a circuit containing a cell and a resistor when a second resistor is added in parallel?
The current through the circuit increases and the total resistance of the circuit decreases to less than the resistor of the smallest one.
What is the method of adding resistors into series?
1) Get at-least 4 identical resistors
2) Build a series circuit with battery and Ammeter and a resistor.
3) Make note of the Pd of the battery then work out resistance using R = V/I to work out resitance
4) Add another resistor and repeat till you have used all resistors.
What is the method of adding resistors into parallel?
1) Build initial circuit as one in series, measure the total current and Pd and use R = V/ I
2) Add another resistor, in parallel
3) Measure Current and Potential difference.
4) Repeat steps 3 and 4.
When plotting the graph for series circuits when adding more resistors to circuit and finding resistance what is the relationship?
Adding more resistors increases the total resistance of the circuit, decreasing the amount of current flowing through the circuit
When plotting the graph for parallel circuits when adding more resistors to circuit and finding resistance what is the relationship?
When adding Resistors in parallel the total current through the circuit increases, so the total resistance of the circuit has decreased. The more resistors you add the smaller the resistance becomes.
What is Dc and where is it supplied to?
This is Direct current which flows in one direction and it is supplied to cells and batteries.
UK mains of electricity is what type of current?
AC changes direction constantly
What is the Frequency of Uk mains?
50 Hz
What is the voltage of Uk mains?
230V
What does Never Entertain lamas stand for?
Neutral
Earth
Live
What colour is Neutral wire and what is its purpose?
It is Blue which is called the neutral wire and this completes the circuit and has a Pd of 0V.
What colour is Earth wire and what is its purpose?
Green / yellow stripes this is the safety wire stopping appliances from becoming live.
What colour is live wire and what is its purpose?
Carries the alternating potential difference from the supply of 230v
Which is the most dangerous wire and why?
The live wire is the most dangerous and could be easily fatal, even if switch is opened, because our body has a potential difference of 0 V, this means if you touch the live wire, a large potential difference is produced across the body and current flows through you.
What is the meaning of power?
How fast energy is converted from one form into another.
What is the formula for power?
P = E/T
P is power in watts
E = energy transferred in Joules
T is time in seconds.
A hair dryer converts 600 j of electrical energy in 5 minutes. Calculate power input?
E = 600 X 1000 = 600, 000 J T = 5 x 60 = 300s P = 2000 W
An incandescent filament bulb is labelled 60 W, while an energy saving bulb is labelled 15 W, both bulbs are equally bright when connected to mains supply. John says ‘the bulb 15 W is better for environment but is unable to explain why’
Both bulbs are producing the same amount of light energy per second. The 60 W bulb is producing heat energy per second. Therefore the 60 W bulbs is wasting more energy.
What is the equation that links Power Current and voltage?
Power = Current X voltage
What is the equation that links Power current and resistance?
Power = Current (squared X resistance)
What is the equation that links Charge flow, potential difference and Energy transferred?
Energy transferred (joules) = Charge flow (Q) X Potential difference.
What is the National Grid?
It consists of Transformers and high voltage cables, it national grid connects power stations to homes.
How does National Grid work?
Step up transformer increases the potential difference, this reduces the energy loss in the transmission cables. Step- down transformers reduce the Potential difference before the electricity passes to homes.
