P2- Electricity Flashcards
Define current
The flow of charged particles
The _ the resistance across a component, the _ the current that flows
Greater
Smaller
What is the equation for total charge
Charge flow = Current X time
What is the equation for potential difference
Potential difference=Current X resistance
What do ohmic conductors have
Constant resistance
What does LDR stand for
Light dependent resistor
What does the resistance of a thermistor depend on
Temperature
What happens to the resistance of a thermistor in different temperatures
Hot goes up cold goes down
How can you use LDRs and thermistors
in sensing circuits
How can sensing circuits be used
To turn on or increase the components depending on the conditions they are in
How are components arranged in a series circuit
Around in a line
What is the equation for total potential difference in a series circuit
Vtotal=V1+V2+…
What is the equation for current in a series circuit
I1=I2…..
What is the equation for total resistance in a series circuit
Rtotal=R1+R2
What is the equation for potential difference in a parallel circuit
V1=V2
What is the equation for current in a parallel circuit
Itotal=I1+I2+…
What does adding a resistor do to the total resistance in a parallel circuit
Reduces the total resistance
What type of supply is the mains supply
AC
What type of battery supply is used
DC
What does AC current do
Constantly change direction
What does DC current do
Constantly flow in the same direction
How many wires do most cables have
3
What are the 3 different wires in most cables
- Live wire
- Neutral wire
- Earth wire
What is the live wire
The wire provides the alternating potential difference from the main supply
What is the neutral wire
The neutral wire completes the circuit- when the appliance is operating normally, current flows through the live and neutral wires
What is the Earth wire
It’s protecting the wiring, and for safety - it stops the appliance casing from becoming live. It doesn’t usually carry a current- only when there is a fault
Can the live wire give you an electric shock
Yes
What is the equation for energy transferred
Energy transferred= Power(w) X Time(s)
What is the equation for energy transferred
E= Charge flow X potential difference
What is the equation for power including potential difference and current
P =VI
What is the equation for power including resistance and current ( this may be wrong)
P=I^2R
What is potential difference changed by
A Transformer
What does a build up of static electricity cause
Friction
When too much static electricity causes a spark what is there a lot of
Potential difference
Similar charges _ ,opposite charges _
Repel
Attract
What do electric charges create
Electric field
Where is an electric field created around
Electrically charged object
How can you show an electric field
Field lines
Charged objects in an electric field fell a _
Force
When are sparks caused
When there is a high enough potential difference between a charged object and the Earth
Define charge
Value of electricity flowing in a circut
Define current
Flow of electrons
Define potential difference
Pushes current around
Define define resistance
Anything that slows down the current
Give two example of when a thermistor may be used
- In a thermistat to turn a heater on below a certain tempreture
- In a freezer to turn on a cooler when the temperature becomes too high
State what happens to the resistance of an LDR as the light intensity increases
The LDR’s resistance increases
Give an application for an LDR
○ Street lights
○ When light levals become too low, the light gains sufficient current to turn on
State the equation linking charge, current
and time. Give the units for the quantities
involved.
Q = I t
Charge (Coulombs), Current (Amperes),
Time (Seconds)
What can be said about the value of
current at any point in a single closed
loop?
Current is the same at all points in a
closed loop
What two factors does the current in a
circuit depend on?
- Potential Difference (V)
2. Resistance (R)
What equation should be used to
calculate potential difference if current
and resistance are known? State the
units for all 3 quantities.
V = I R Potential Difference (V), Current (A), Resistance (Ω)
What is an ‘Ohmic Conductor’? State the
condition required.
● A conductor for which current and potential difference are directly proportional ● Resistance remains constant as current changes ● Temperature must be constant
List four components for which
resistance is not constant as current
changes
- Lamps
- Diodes
- Thermistors
- Light Dependant Resistors (LDRs)
What happens to the resistance of a
filament lamp as the temperature
increases? Why?
● Resistance increases
● Ions in metal have more energy, so vibrate
more, causing more collisions with
electrons as they flow through the metal,
creating greater resistance to current flow
What is different about current flow
through a diode?
● The current only flows in one direction
● Resistance is very high in the other
direction, preventing current flow
State what happens to the resistance of
a thermistor as temperature increases.
The thermistor’s resistance decreases.
Give two examples of when a thermistor
may be used.
- In a thermostat to turn a heater on
below a certain temperature - In a freezer to turn on a cooler when
the temperature becomes too high
State what happens to the resistance of
a LDR as light intensity decreases.
The LDR’s resistance increases.
Give an application for a LDR.
● Street lights often use LDRs
● When light levels become too low, the
light gains sufficient current to turn on
What are the two ways that a component
can be connected in a circuit?
- Series (same loop)
2. Parallel (adjacent loop)
How does the potential difference across
two components vary when connected in
series and parallel?
● Series: Total P.D is shared between
each component
● Parallel: P.D across each component
is the same
If two resistors are connected in parallel,
what can be said about their combined
total resistance?
Their total resistance is less than the
smallest of the two individual
resistances.
If two resistors are connected in series,
what can be said about their total
resistance?
Their total combined resistance is equal
to the sum of the two individual
resistances
Describe the current in a series circuit.
In a series circuit, the current is the same
at all positions since the charge only has
one path to flow through.
Describe the current in a parallel circuit.
In a parallel circuit, the current is shared
between the different branches. When
the charge reaches a junction it splits.
How should you connect an ammeter in a circuit to
measure current?
Ammeters should be connected in series
with the component that they are
measuring current through.
How should you connect a voltmeter in a
circuit to measure potential difference?
Voltmeters should be connected in
parallel to the component that they are
measuring the potential difference of
Why is it advantageous to connect lamps in parallel?
If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete).
Is mains electricity an a.c supply or a d.c
supply? What do each of these stand
for?
Mains electricity is an a.c supply
a. c. : Alternating Current
d. c. : Direct Current
Define alternating current and direct current.
● Alternating current: Current that continuously changes direction at a specific frequency ● Direct current: One directional current flow
What is the frequency and voltage of the UK mains
electricity supply?
● Frequency: 50 Hz
● Voltage: 230V
How many wires are usually in the cables connecting
electrical appliances to the mains? Name these
wires.
- Live wire
- Neutral wire
- Earth wire
State the insulation colour used on the Earth wire.
Green and Yellow Stripes
State the insulation colour used on the live wire
Brown
State the insulation colour used on the Earth wire.
Blue
Explain when the Earth wire does and doesn’t carry
a current.
● Under normal circumstances, no current
flows through the Earth wire
● If a fault occurs in the appliance (such as a
surge or the casing becoming live), current
will flow to the ground
What potential is the neutral wire at?
0 Volts
State the potential difference between the live and
earth wires.
230 Volts
What is the purpose of the neutral wire?
To complete the circuit by connecting the
appliance back to the mains supply.
For metal appliances, where is the Earth wire
connected to? Why?
● Earth wire is connected to the metal casing
of the appliance
● If live wire becomes loose and touches the
casing, the current will flow through the
Earth wire, preventing electrocution
State two equations for the power of a circuit. Give
appropriate units.
P = I V P = I² R
Power (Watts), Current (Amperes)
Potential Difference (Volts), Resistance
(Ohms)
State an equation linking energy transferred, power
and time. Give appropriate units.
E = P t
Energy (Joules), Power (Watts), Time
(Seconds)
State an equation linking energy transferred, power
and time. Give appropriate units.
E= Q V Energy (Joules), Charge (Coulombs), Potential Difference (Volts)
What two main factors does the amount of energy
transferred by an appliance depend on?
- How long the appliance is being used
for - The power of the appliance
Describe the energy transfers in a battery powered
torch.
● Battery converts chemical energy into electrical energy ● Bulb converts electrical energy into light as well as waste energy in the form of heating
Describe the energy transfers in a battery powered
motor.
● Battery converts chemical energy into electrical energy ● Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
What three things determine the power of a circuit
device?
1. The potential difference across the circuit 2. The current through the circuit 3. The amount of energy transferred in a given time
What is the purpose of the National Grid?
To link power stations to consumers so
that they have access to a source of
electricity.
What are the two types of transformers used in the
National Grid?
- Step-Up Transformers
2. Step-Down Transformers
Where are step-up transformers found in the
National Grid? What do they do?
● Step-Up Transformers are used when
connecting power stations to
transmission cables
● They increase the potential difference
Where are step-down transformers found in the
National Grid? What do they do?
● Step-Down Transformers are used in
connecting transmission cables to
domestic buildings (like houses)
● They decrease the potential difference
Why do transmission lines transfer electricity at high
potentials?
● A high potential, results in a low current
● The lower the current, the less energy
that is wasted as heat
● Therefore it is more efficient
Why does the potential need to be decreased
between transmission lines and houses?
● Lower potentials are safer for domestic
use and reduces the likelihood of
severe electrocution
● Appliances are designed for 230V
What can happen when insulating
materials are rubbed together?
They can become (statically) electrically
charged.
Why can insulators become electrically charged
when rubbed together?
● Electrons are rubbed from one material onto the
other
● The material gaining electrons becomes
negatively charged
● The material losing electrons becomes equally
positively charged
What happens when two electrically charged objects
are brought close together?
They exert a force on each other
What happens when two identically charged objects
are brought close together?
They exert a repulsive force on each
other and repel.
What happens when two oppositely charged objects
are brought close together?
They exert an attractive force on each
other and attract.
Give an example of a non-contact force.
The repulsive or attractive force acting
between two electrically charged objects.
What is an electric field?
A region in which a charged object will
experience a non-contact electrical force.
Where can electric fields be found?
Surrounding any charged object.
Describe the electric field around a
charged particle.
● Strongest closest to the object
● Decreases in strength as you move
away from the object
What happens to the force between two charged
objects when they are moved closer together?
The force between them becomes
stronger as the separation reduces.
In situations where sparks are unwanted,
what precaution must be taken to
prevent the build up of static charge?
Any surfaces that are rubbing against
each other should be earthed to allow
the charge to flow off the materials.
