Topic 10 - Electricity & Circuits Flashcards
What 3 subatomic components make up an atom?
Electrons
Protons
Neutrons
Describe the structure of an atom
Neutrons and protons in nucleus
Electrons surrounding nucleus in shells
What are the charges of the particles in an atom
Proton +1
Neutron 0
Electron -1
In a closed circuit, if there is a potential difference in the circuit there will also be a…
Current
How is current defined
As the rate of flow of charge (or electrons) round a circuit
What are the units of charge
Coulombs (C)
What are the 2 ways that a component can be connected in a circuit
Series (same loop)
Parallel (adjacent loop)
Voltage is also known as…
Potential difference
How does the potential difference across 2 components vary when connected in series and parallel?
In series circuit, total PD is shared between each component
In parallel circuit, PD across each component is the same
If 2 resistors are connected in parallel, what can be said about their combined total resistance
Total resistance is less than the smallest of the 2 individual resistances
If 2 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 indiviso resistances
Where must a voltmeter be placed in a circuit
In parallel with the component that is being measures
Give an equation relating potential difference with energy transferred and charge
Potential difference (V) = energy transferred (J) / charge (C)
V = E/Q
A volt can also be described as…
Joule per coulomb
What is an electric current
The rate of flow of charge
State the equation linking charge, current and time. Give the units for the quantities involved
Q = I t
Charge(coulombs), Current(amperes), Time(secs)
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 2 factors does the current in a circuit depend on?
Potential difference (V) Resistance (R)
What equation supuld be used to calculate potential difference if current and resistance are known?
V = I R Potential difference (V) = Current (A) x Resistance (Ohms)
Whats an ammeter and where must it be connected in a circuit?
Measures current.
Placed in series with component its required to measure.
What happens when current reaches a junction in a circuit?
Current is conserved.
The total current remains the same and is split between the two branches.
How does resistance affect current in a circuit?
As the total resistance of a circuit increases, the current flowing through the circuit decreases
How can the current in a circuit be varied
Using a variable resistor
Give the equation linking current with resistance
P.D. (V) = current (A) x resistance (Ohms)
V = I R
How is total resistanve affected by 2 resistors in series
Total resistance increases
Is equal to the sum of 2 resistors
How is total resistance affected by 2 resistors in parallel
Total resistance decreases
Is less than the resistance of the resistor with lowest resistance
Whats an Ohmic Conductor. State conditiom required.
Conductor for which current and pd are directly proportional
Resistance remians constant as current changes
Temp must be constant
List 4 components for which resistance isnt constant as current changes
Filament lamps
Diodes
Thermistors
Light dependant resistors (LDRs)
What happens to resistance of a filament lamp as the temperature increases? Why?
Resistance increases
Metal ions have more kinetic energy so vibrate more, colliding more frequently with electrons as they flow through metal
This creates more resistance to current flow
Whats different about current flow through a diode?
Current only flows in one direction
Resistance is very high in other direction, preventing current flow
State what happens to the resistance of a thermistor as temperature increases
The thermistors resistance decreases
Give 2 examples of when a thermistor may be used
In a thermostat to turn a heater on below a certain temp
In a freezer to turn on a cooler when the temp becomes too high
State what happens to the resistance of an LDR as light intensity decreases
The LDRs resistance increases
Give an application for a LDR
Street lamps or night lights
When light levels drop (night) resistance increases and the light gains sufficient current to turn on
How do diodes work?
A diode only allows current to flow in one direction. If current is flowing right way, resistance is large for small voltages (uo until 0.6V) but then higher voltages become very small.
What electrical component does this graph represent? —|-/
Diode
What factors affect the energy transferred when charge flows through a component?
Amount of charge
Pd across the component
Give an equation linking energy, current and pd
Energy (J) = pd (V) x current (A) x time (s)
E = V I t
Define potential difference in terms of charge
The work done per unit charge
Give an equation relating potential difference to charge
Energy transferred (J) = charge (C) x pd (V) E = Q V
When an electrical current flows through a resistor why does it heat up?
There are collisions between the electrons and ions in the resistors lattice. This causes a transfer of kinetic energy into thermal energy, which is released into the surroundings.
How do low resistance wires reduce unwanted energy transfers
A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating
What are some advantages of the heating effect
Its useful for appliances such as toasters or electrical fires, where the heat is the desired product
What are some disavantages of the heating effect
Loss of energy as heat energy can make an appliance inefficient
If an appliance overheats it can catch fire or overheat which could ruin the device or injure user
The energy transferred per second is also known as
Power
Define power
The rate of energy transfer, or rate at which work is done
What are the units of power
Watts W
Give equation linking power and pd
Power (W) = current (A) x pd (V)
P = I V
Give equation to work out power without pd
Power (W) = current squared (A) x resistance (Ohms)
P = I2 R
Give an equation linking power and energy
Power (W) = energy (J) / time (s)
P = E/t
Give both equations linking power with resistance
Power (W) = current squared (A) x resistance (Ohms)
P = I2 x R
Power (W) = pd squared (V) / resistance (Ohms)
P = V2 / R
What word describes materials that electricity will pass through?
Conductors
What word describes materials that electricity cannot pass through?
Insulators
What components do you need to make a circuit that would make a small torch bulb light up?
Battery, connecting wires, lamp, switch is optional
What are the two terminals of an electric cell labelled as?
Plus and minus
In an electric circuit with a battery, which of these materials will conduct: copper, wood, salty water
Copper and salty water
Which of these materials are insulators? Plastic metal air
Plastic and air
What name is given to the negatively charged subatomic particles that cause an electric current?
Electrons
Is mains voltage about 15 times, 150 times or 1500 times bigger than the voltage from a battery?
About 150 times
If you connect some cells together in series, what forms
A battery
Which line on the cell is the negative terminal
Shorter line
Whats the difference between convectional current and flow of electrons?
Electrons flow from negative terminal of cell to positive terminal, convectional flows the other way
What 2 conditions are needed to give a current in a circuit?
Closed circuit and potential difference
What is current measured in
Amps/amperes
What does AC mean?
Alternating current
What is alternating current?
Current which is constantly changing between a negative and positive maximum
What does DC mean?
Direct current
What is direct current?
Current which takes a constant value
Is mains electricity an AC or DC supply?
AC supply
What is meant by the frequency of a supply?
The rate at which an AC current changes
Whats the frequency and voltage of the UK mains electricity supply?
Frequency: 50Hz
Voltage: 230V
What type of current do batteries and cells supply?
Direct current
What is the power rating of an appliance?
Shows how much energy a device converts per second
What wires does a typical domestic appliance have?
Live wire
Neutral wire
Earth wire
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Green and yellow stripes
Explain when the Earth wire does and doesnt carry a current
Under normal circumstances, no current flows through wire
Current flows when a fault occurs in the appliance
What potential is the neutral wire at?
0 volts
State the potential dofference 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?
Metal casing of appliance
If live wire touches the casing, current will flow through earth wire preventing electrocution
How does a fuse stop a device getting damaged?
When current gets too high
fuse wire melts and breaks
stopping current flowing to appliance
preventing damage
Why is it important to connect a fuse or switch to live wire
When switch turned off/fuse breaks it will break the circuit and stop current flowing through wire.
This provides a method to stop current flowimg into the appliance.
Why is it dangerous to have a connection between the earth wire and live wire?
Can result in current surge, causing electrical shocks
What is a current surge?
When significantly more current comes through the wire
