Chapter 10- Electricity and circuits Flashcards
Describe the structure of an atom
An atom consists of negatively electrons surrounding a nucleus that contains positively charged protons and 0 charged- neutral- neutrons.
What is the difference between a series and parallel circuit
Series- when current is flowing through, at each component amount will be the same. When voltage is flowing through then they will be different at each component but add together to = supply voltage.
Parallel- when current is flowing through they will be the same when on a parallel together, when voltage is flowing through they will all be equal (same at each component)
What is said to describe the current in a parallel connected circuit
The current is described as being conserved.
What is a voltmeter used to in a parallel circuit
A voltmeter is connected in parallel with a component to measure the potential difference (voltage) in volt, across it.
What is potential diference
potential difference (voltage) is the energy transferred per unit charge passed and hence that the volt is a joule per coulomb
What is the equation for energy transferred IN A CIRCUIT?
E
Q V
What does the letter ‘V’ stand for
potential difference- measured in volts
What does the letter ‘Q’ stand for
Charge moved (Coulomb)
What is an ammeter used for in a series circuit
An ammeter is connected in series with a component to measure the current, in amps, in the component.
What is an electric current
An electric current is the rate of flow of charge and the current in metals is a flow of electrons
What is the equation for charge?
Q
I t
What does the letter ‘I’ stand for
current (ampere)
What is present when a closed circuit includes a source of potential difference
There will be a current in the circuit
Where is current conserved
Current is conserved at a junction in a circuit
What happens when you change the resistance in a circuit
Changing the resistance in a circuit changes the current and this can be achieved using a variable resistor/
What is the equation for potential difference(volts)
V I R(ohm)
What happens if 2 resistors are in a series circuit
The net resistance is increased
What happens if 2 resistors are in a parallel circuit
The net resistance is decreased
Explain the design and construction of series circuits for testing and measuring
x
Describe the core practical when constructing electrical circuits to investigate the relationship between potential difference, current and resistance for a resistor and a filament lamp
Set out a circuit where an ammeter and variable resistor is in series and a volt meter in parallel.
The variable resistor varies the resistance and we use the ammeter to measure the current Change
Describe the core practical when constructing electrical circuits to test series and parallel circuits using resistors and filament lamps
x- is it the compulsory practical in our books?
How does current vary with potential difference in filament lamps
The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it, it is said to follow ohms law. However the lamp wont follow ohms law when resistance increases ??? X
How does a filament lamp produce light
The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.
Explain how current varies with potential difference in diodes
The diode has a very high resistance in one direction. This means that current can only flow in the other direction, it is a non ohmic conductor
How can we tell from a graph when something is non ohmic (doesn’t obey ohms law?)
When its not a straight line
What is ohms law
The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. So if you double the voltage, the current also doubles
What is resistance measured in
ohms
What is a diode
It allows current to flow in one direction only. It is a polarised component with two leads, called the cathode and the anode.
What is forward bias
If the anode is connected to a higher voltage than the cathode, the current will flow from anode to cathode= forward bias.
What is reverse bias
If the diode is put in the circuit back to front the voltage at the cathode will be higher than the voltage at the anode, the diode will not conduct electricity= reverse bias
How does current vary with potential difference in fixed resistors
Current is directly proportional to the potential difference
What does the resistance of a light-dependent resistor depend on
Resistance of a LDR varies with light intensity. Using light sensitive circuits-
In the dark and at low light levels, the resistance of an LDR is high and little current can flow through it. In bright light, the resistance of an LDR is low, and more current can flow through it.
Uses of an LDR
automatic security lights
controlling how long the shutter should remain open on a digital camera- changes in resistance are measured, if levels of light are low the shutter stays open for longer
What does resistance of thermistor depend on
Varies with change of temperature, At low temperatures the resistance of thermistor is high and little current can flow through them. At high temperatures, the resistance of a thermistor is low, and more current can flow through them
Uses of thermistors
Used as temperature sensors eg- fire alarms as when temperature increases their resistance is lower and so more current can flow through
How can the design and use of circuits be used to explore the variation of resistance in FILAMENT LAMPS
x
What happens when there is an electric current in a resistor
When there is an electric current in a resistor, there is an energy transfer which heats the resistor
Why is electrical energy dissipated as thermal energy in the surroundings
Electrical energy is dissipated as thermal energy in the surroundings when an electrical current doesn’t work against the electrical resistance
When there is an electric current in a resistor why is there an energy transfer which heats the resistor?
It is a result of collisions between electrons (from loose electrons in outer shells in metals) and the ions in the lattice. Each of these collisions causes energy to transfer to the lattice in the form of heat as a result the metal heats up.
Explain ways of reducing unwanted energy transfer
XXXXXX
Using low resistance wires
Describe the advantages and disadvantages of the heating effect on the electric circuit
Heating water in a kettle ad electric fires are results in the resistor heating up.
But it isn’t always useful, when too much current flows through wires, they can become too hot and catch on fire or bur the user.
What is the energy transferred equation
E= I x V x t
Describe power
The energy transferred per second (measured in watts)
What is the power equation
E
P t
Explain how the power transfer in any circuit device is related to the potential difference across it and the current in it
X
What is the electrical power formula?
P
I V
What is the 2nd version of the electrical power formula?-
How do you know when to use it?
P
I2 R
Replace the V with I squared (current squared)
How is energy transferred from batteries and the a.c. mains to the energy of motors and heating devices
eg-
electric motors transfer electrical energy into kinetic energy, using magnets and coils of wire
XXXXXXXX
Describe the difference between direct and alternating current
DO WE NEED TO KNOW ALTERNATING/DIRECT VOLTAGE TO?
If the current only flows in one direction only then it is called a direct current, if the current constantly changes direction it is called an alternating current
Describe direct current
Movement of charge in one direction only, cells and batteries supply a direct current (d.c)
Describe an alternating current
Movement of charge changes direction, motors often work by using alternating currents, it is easily changed with a transformer and can be transferred efficiently over large distances.
What is the UK domestic supply, at what frequency and what voltage?
The UK domestic supply is a.c, at a frequency of 50Hz and a voltage of about 230V
Explain the difference of function between the live and neutral mains input wires
The live wire carries a current that alternates between a negative and positive voltage, the neutral wire completes the circuit and carries the current away from the appliance . It is kept at 0 voltage by the electricity company.
What are the colours of the 3 types of wires?
The live- brown
The earth- green
The neutral- blue
Explain the function of fuses in ensuring safety
If a fault occurs where the live wire connects to the case, the earth wire allows a large current to flow through the live and earth wires. This overheats the thin wire in the fuse which breaks the circuit when current is to high.
Appliance stops working if danger occurs, the fuse acts as an early warning system which prevents damage by surges in electricity.
Describe the function of the earth wire and how it ensures safety
A safety wire to earth appliances with a metal case, When a loose live wire touches the metal part of an appliance, the electric current will flow to the ground via the earth wire, this prevents the person who touches the metal part of the appliance from getting an electric shock.
Explain function of circuit breakers in ensuring safety
Found in a fuse box, each circuit breaker is an electromagnetic switch which is designed to break the circuit when the current gets too high. Too much current makes the magnetic field produced by the electromagnet strong enough to open the switch, the circuit breaker is said to ‘trip and switch off the current’
Why do appliances such as hair dressers not need earth wires
Hairdryers are said to be double insulated, and there’s no need for an earth wire because the case is made of a non conducting plastic. If a faulty live wire touches the inside of the plastic case there is little rick as the case is an insulator.
what are earth wires made of
copper
Why switches and fuses should be connected in the live wire of a domestic circuit
If too much current flows the fuse wire overheats and melts, breaking the circuit. They should be connected to the live wire because this disconnects the appliance from the electricity source which makes it safe for a person to touch without risk of electrocution.
What fuse should you use? List available fuse options and how to find out
XXXXXXX
P I V
Explain dangers of providing any connection between the live and earth wire
XXXXXX
you can get an electric shock if the live wire inside appliance such as a cooker comes lose and touches metal casing,
Describe the relationship between power ratings for domestic electrical appliances and the changes in stored energy when they are in use
XXXXX
The more energy that is transferred in certain time, the greater the power.
Why is resistance decreased in parallel circuits
More current flows from source than would flow for any of them individually so total resistance is lower
What’s resistance proportional to
Resistance is proportional to length of wire / by cross sectional area
What does the resistance tell us
The potential difference required to drive a current through a component
What is resistance…c
Constant, doesn’t change if we increased current = ohmic conductor as current through a resistor is directly proportional to potential difference
