Electricity Flashcards
What is electrical current?
Electrical current is the flow (movement) of electric charges.
what does there have to be for electrical charge to flow?
there has to be a source of potential difference and a closed (or complete) circuit.
What is electric current measured in?
Amperes (A)
What is the equation for the flow of charge?
The flow of charge (C) = current (A) x time (s)
What is the value of the current like in a single closed loop?
A current has the same value at every point in a single closed loop.
What is the equation for current?
current = charge / time
Calculate the charge that has flowed past a point in the circuit if the current of 2A has been flowing for 3 seconds…
- Remember the equation for charge.
Q = I × t - Substitute the values in.
Q = 2 × 3 - Write the answer, remembering to include an appropriate unit.
Q = 6 C
What is an electrical insulator?
a material which doesn’t allow electric currents (flow of electric charges) to pass through it
-E.g. Glass and Plastic
What are electrical conductors?
a material that allows electric current (flow of electric charge) to pass through it
-E.g. All metals
what does the free electron inside electrical conductors allow?
The free electrons inside electrical conductors explain why they can conduct electricity.
Why don’t electrical insulators conduct electricity?
an electrical insulator has no free electrons so no charges are free to move and carry a current
Why do electrical conductors conduct electricity?
- Have lots of charges which are free to move
- In a metal, the charges that are free to move are electrons
- the electric current through the metal is the flow o these electrons
What charges are free to move in metals?
Electrons
The movement of electric ………… is the basis of electrical current
charges
Current = charge / time
How would you rearrange this equation if you wanted to calculate charge?
Charge = current x time
An electrical conductor has lots of …………….. that are free to move.
charges
What is potential difference?
Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.
What is potential difference measured in?
Volts (V) -also called voltage
What instrument do you use to measure a potential difference?
a voltmeter (V)
When is energy transferred to the electrical components in a circuit?
The energy is transferred to the electrical components in a circuit when the charge carriers pass through them.
What is the equation for potential difference?
potential difference = current x resistance
If voltage is 10V and charge is 2C, what is the energy transferred?
- Remember the equation for voltage
Voltage = Energy ÷ Charge - Rearrange the equation
Energy = Voltage × Charge - Substitute in the numbers
10V × 2C = 20 J
A potential difference of one Volt is equal to one ……….. of energy being used by one ……………. of charge when it flows between two points in a circuit.
- Joule
- Coulomb
what does an ammeter measure?
The flow of current that passes through it
Ammeters have to connected in ………….. (In the same loop of the circuit) with the electrical component whose current you are measuring.
- series
What do voltmeters measure?
measure potential difference (voltage) between two points in a circuit
Voltmeters must always be connected in ………….. (on a separate branch of the circuit) with the two points being measured.
paralelle
What instrument is used to measure current?
an ammeter
An ammeter must be connected in …………. with the components you want to measure and a voltmeter must be connected in ……………..
- series
- parallel
The potential difference is the difference in the amount of energy that charge carriers have between two points in a …………… . Potential ……….. (p.d.) is measured in …………… and is also called voltage
- circuit
- difference
- Volts
when charge flows in an electric circuit, the size of the current is a affected by which 2 things?
- The resistance: if the resistance is increased, the current will decrease
- The potential difference: if the potential difference is increased the current will increase
what is resistance measured in?
ohms
What variables affect the size of a current?
- Resistance
- Potential difference
Resistance is a measure of the…
difficulty of the flow of current through a component
what is the equation for resistance? (Ohms law)
R = V/I resistance = potential difference / current
how do we measure resistance across a component? (lamp or resistor)
measure the potential difference across the component
We calculate potential difference using a …………. and current using an ……………… at the same time.
- voltmeter
- ammeter
what do we use an ammeter to measure?
the current flowing through a component
how does the length of the wire affect resistance?
the longer the wire, the higher the resistance
To measure the resistance of a component in a circuit, measure the …………….. difference across the component and the current flowing through the component.
-potential
what is an ohmic conductor?
An Ohmic conductor is a conductor that obeys Ohm’s Law
what is the current through an ohmic conductor directly proportional to?
this means that…
the potential difference across the resistor
… the resistance remains constant as the current changes
what is a conductor in a circuit?
a conductor is any electrical component which conducts electricity
what is the ohms law equation? (Resistance)
potential difference = current x resistance
In an Ohmic conductor, the resistance…
remains constant
How would Ohm’s Law be rearranged to calculate potential difference?
potential difference = current x resistance
When the potential difference is 10V and the current is 2A, what is the resistance?
- Remember the equation for resistance
R = V ÷ I - Substitute the values in
R = 10V ÷ 2A - Write out answer
R = 5Ω
We can plot a current-voltage graph by varying theacross a circuit component
- potential difference
The current-voltage graph for a resistor
has a …………. line obeying …………….. Law:
The slope of the graph is equal to 1/……………….
The constant slope (straight line graph) tells us that the resistance is ……………..
- straight
- Ohm’s
- resistance
- constant
current = potential difference/……………………….
resistance
What effect will increasing the current through a filament bulb have on a graph?
the line will curve because the temperature and resistance are rising
What is resistance a measure of?
how difficult it is for current to flow through a component
To measure resistance you need 3 things:
- an ammeter in series
- a voltmeter in parallel
- Ohm’s law
The current through an Ohmic ……………… (at a constant temperature) is directly proportional to the …………… difference across the resistor.
- conductor
- potential
the current of an electrical circuit can be calculated using what equation?
current (measured in amperes) = potential difference (measured in volts) / resistance (measured in ohms).
what is current measured in?
amperes
what is potential difference measured in?
volts
what is resistance measured in?
ohms
What would you use to measure potential difference across a component?
a voltmeter
If the resistance is increased, the current will ………………… if the potential difference is kept constant. If the potential difference is increased the current will ………………… if the resistance is kept constant.
- decrease
- increase
On a current-voltage graph for a resistor, the slope of the graph is equal to 1/……………..
-resistance
In an electrical circuit, what makes the current flow?
How?
-the energy source (battery or power supply) makes a current flow
It provides electrical energy to a bulb which radiates that energy as light and heat energy.
A light bulb is rated at 3V and draws a current of 2A. The bulb is on for 10 seconds. How much electrical work is done on the light bulb?
-Remember the equation for electrical work done
E = P × t = I × V × t
-Substitute the values in
E = 2 × 3 × 10
- Write the answer, remembering to include the appropriate unit
E = 60 J
power is equal to the …………… squared multiplied by the ……………..
- current
- resistance
Charge flows from the energy source to the rest of the circuit and its components, like lamps and heaters. The flow of current transfers ……………… from the energy source to the …………………..
- energy
- components
in circuit diagrams what do straight lines show?
wires connecting the opponents
what do circuit diagrams represent?
circuits
What is the symbol for a motor?
a circle with an M in in
name two common mistakes when drawing circuits…
- breaks in the lines that you use to represent wires
- wires passing through the components
what is a diode?
Diodes
A diode is a component that only allows current to flow through it in one direction.
what is a rectifier?
a component that turns an alternating current (repeatedly changes direction) into a direct current (One direction)
Diodes act as ………………. as they block the ……………… current when it changes direction
- rectifiers
- alternating
The current through a diode only flows in …………. direction. In the reverse direction, the resistance is very ………………..
- one
- high
what are thermisters and LDRs and what can they be used for?
Thermistors and LDRs are devices where resistance changes with temperature or light. They can be used as switches for heaters and lights
What is a thermister?
a component that’s resistance changes with its temperature
-usually, increasing temperature decreases resistance
what can we use a thermister for?
- to turn a heater off when a house reaches certain temperatures
- fire alarms
what are LDRs?
a light dependent resistor which changes with light intensity
-usually, increasing light intensity decreases resistance
what do we use LDRs for?
to switch lights on when it gets dark or to know whether or not a camera phone needs to use “flash”
If a thermistor is connected in series with a resistor and battery, what will happen in the circuit when the temperature increases?
- decreased resistance of the thermister
- increased potential difference across the resistor
What effect will increased light intensity have on an LDR?
decreased resistance
A ……………. circuit has all its components connected on the same line as each other.
series
In a series circuit, the current is the ……………. at all points in the circuit
same
The charge flows through the circuit like water flows through pipes.
The amount of water entering one end of a pipe is the …………… as the amount leaving the other end
same
In series circuits, the resistors all oppose the flow of electric current through the circuit. how are their total resistance calculated by?
Their total resistance is calculated by adding up the resistances of each individual resistor: R = R1 + R2 + R3 +….
What is the resistance of two 10 Ohm resistors in series with three 2 Ohm resistors?
- Remember the formula for the combined resistance of resistors in series
R = R1 + R2 + R3 - Substitute the values in
R = (2 x 10) + (3 x 2) - Write the total resistance, remembering to include an appropriate unit
R = 26 Ohms
how is a battery made?
by joining cells together
how is the potential difference (energy that drives a current to flow through a circuit) of three energy sources in series found?
by adding up their individual voltages:
V = V1 + V2 + V3 …
the total ………………. of a set of resistors is the sum of the individual …………………….
- resistance
- resistances
What is the total potential difference supplied to a circuit when 2 cells, each with a potential difference of 5V, are connected in series?
- Remember the equation for total potential difference
VTotal = V1 + V2 - Substitute the values in.
VTotal = 5 + 5 - Answer
VTotal = 10 V
Total voltage of energy sources = total …………………… ……………….. across components
potential difference
What are the key features of a series circuit?
- All components are attached in a row.
- The current is equal everywhere in the circuit.
- The voltage across each component is different.
- The sum of the voltages across each component is the total battery voltage
What is the resistance of five 10 Ohm resistors in a series circuit?
- Remember the formula for the combined resistance of resistors in series
R = R1 + R2 + R3 + R4 + R5 - Substitute the values in
R = 5 x 10 - Write the total resistance, remembering to include an appropriate unit
50 Ohms
How does current change around a series circuit?
it doesn’t
A ……………… circuit is where there is only one loop of wire, and all the components are on it.
series
what happens to the current in a series circuit?
the current is the same at all points in the circuit
In a …………………. circuit, components are connected on separate branches of wires to the energy source
parallel
In a parallel circuit, components are connected on separate branches of wires to the energy source. The current through the battery is …………………. than the current through each of the individual branches.
larger
In a ………………. circuit the current through the energy source is equal to the sum of (adding up all of) the currents in the separate branches.
parallel
In a parallel circuit the current through the energy source is ………………… to the sum of the currents in the separate branches
equal
The combined resistance of two resistors in parallel is ………….. than the resistances of either of the two resistors by themselves
less
In the lighting circuit of your house, each lamp is connected to the energy supply in parallel. What are the two main advantages of this?
- Each lamp may be switched on and off separately
- if one lamp stops, current still flows through the others
In the lighting circuit of your house, each lamp is connected to the energy supply in ………………..
paralelle
How do you calculate the total current through the energy source? (in paralle)
it is the sum of the currents in the individual branches
Resistors in parallel are like water draining out of a bucket with a hole. If a second hole is drilled into the bucket the water (like adding another resistor in parallel) will drain ………….. It does not matter how narrow the second hole is (how high its resistance is), it is always ……………. for water to flow through two holes instead of one.
- faster
- faster
is voltage split by the branches in a parallel circuit?
no
Parallel circuits have two advantages over series circuits. Firstly, each component may be switched on and off ……………. , and secondly, if any one component breaks, current ……………… flow through the other components
- separately
- can
what are the 2 types of electrical current?
- direct
- alternating
what is the frequency of mains electricity?
50 Hz
what is the voltage of mains electricity?
230 V
What does AC stand for and what is it?
- Alternating Current
- When the electric current repeatedly changes direction
What does DC stand for and what is it?
- Direct Current
- When the electric current flows in only one direction
what colour is the neutral wire?
blue
what colour is the earth wire?
green and yellow stripes
what wire is the safety wire which stops the appliance becoming live?
the earth wire
what is the potential of the earth wire?
0V
What is the potential of the neutral wire?
close to 0V
what is the purpose of the neutral wire?
completes the circuit and carries current away from the appliance
what is the purpose of the earth wire?
it is a safety wire and stops the appliance becoming live
what colour is the live wire?
Brown
what is the potential of the live wire?
230V
what is the purpose of the live wire?
provides the alternating potential difference from the mains electricity supply
How much energy does a 50W bulb use per second?
50J
What is the current required by an appliance of power 460W if it is plugged into the mains?
- Remember the equation for power
P = V × I - Rearrange to give current
I = P ÷ V - Remember the potential difference across a mains socket
V = 230 Volts - Substitute the values in.
I = 460 ÷ 230 - Answer
I = 2 A
what is the national grid?
The National Grid is the network of cables and transformers that connect power stations with houses and shops in the United Kingdom.
Earth wires are needed for appliances with what?
metal casing
A …………. wire can still be dangerous when the mains switch is open (i.e. the plug socket or light switch is turned off).
live
If you touched the…….. wire, your body would supply a link between the supply and the ground. This is an ………… shock.
- live
- electric
What are the advantages of circuit breakers over fuses?
Fuses only work once. Once blown, they must be replaced. We can reset circuit breakers. Circuit breakers also break circuits faster than fuses. This reduces the risk of getting an electric shock even more.
what are circuit breakers?
Circuit breakers are special devices that switch off the flow of current if the current is higher than a certain value
what s charge measured in?
coulombs
how to objects become charged?
by losing or gaining electrons (Positively or negatively)
opposite charges ………………
attract
What charge will a material gain if it loses electrons?
positive
What charge will a material gain if it gains electrons?
negative
A plastic rod will be charged by rubbing it with a ………….. It will then, attract or ……… other charged objects depending on their charge.
- cloth
- repel
Suggest why clothes dried in a tumble drier might stick to each other.
The clothes will rub against each other in a tumble drier. This could charge the clothes as electrons are lost when the clothes rub together. Some will lose electrons and become positively charged and others will gain electrons and become negatively charged. The clothes that are oppositely charged will attract each other and stick together.
what does static electricity arise?
Static electricity arises when electrons transfer from one object to another.
When electrons transfer from one object to another, one object becomes …………. and one becomes negative.
-positive
Charged objects create electric …………. around them
fields
How can you see electric fields?
you can’t
what are the electric field lines around tiny positively charged and negatively charged objects called?
point charges
