2 - Electricity

What is the symbol for an open switch?

What is the symbol for a closed switch?

What is the symbol for a cell?

What is the symbol for a battery?

What is the symbol for a diode?

What is the symbol for a resistor?

What is the symbol for a variable resistor?

What is the symbol for an LED?

What is the symbol for a lamp ?

What is the symbol for a fuse?

What is the symbol for a voltmeter?

What is the symbol for an ammeter?

What is the symbol for a thermistor?

What is the symbol for an LDR?

What is needed for electrical charge to flow through a closed circuit?

The circuit must include a source of potential difference

What is electric current?

Electric current is a flow of electrical charge

What is the size of the electric current equal to?

The size of the electric current is the rate of flow of electrical charge

What is the equation that links charge flow, current and time?

Charge flow = current x time

What is charge flow measured in?

Coulombs (C)

What is current measured in?

Amperes (A - amps)

What is time measured in?

Seconds (s)

What is the value of current at any point in a single closed loop - series circuit?

A current has the same value at any point in a single closed loop.

What 2 factors does the current through a component depend on?

The resistance and the potential difference across the component

What is the relationship between resistance of a component and the current across it?

The greater the resistance of the component the smaller the current for a given potential difference across the component.

What is another word for potential difference?

Voltage

What is the equation for potential difference using current and resistance?

Potential difference = current x resistance (V = IR)

What is potential difference measured in?

Volts (V)

What is resistance measured in?

Ohms (Ω)

Can the resistance of a component change?

For some resistors, the value of R remains constant but that in others it can change as the current changes.

What is the current through an ohmic conductor at constant temperature proportional to?

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor - as the current changes, the resistance remains constant

What happens to the resistance when the current changes through components such as lamps, diodes, thermistors and LDRs?

The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.

What happens to the resistance of a filament lamp as the temperature increases?

The resistance of a filament lamp increases as the temperature of the filament increases.

What direction does the current through a diode flow?

The current through a diode flows in one direction only.

What happens to the resistance when current flows in the reverse direction through a diode?

The diode has a very high resistance in the reverse direction.

What happens to the resistance of a thermistor as the temperature increases?

The resistance of a thermistor decreases as the temperature increases.

What are some application of thermistors, and how do they work?

They can be used in a thermostat - It changes the resistance every time the temperature changes (when the temp rises, resistance decreases) - this change is measured by the thermostat, which adjusts the heating or cooling system to maintain temp set by user

What happens to the resistance of LDR as light intensity increases?

The resistance of an LDR decreases as light intensity increases.

What are some applications of LDRs in circuits, and how do they work?

They can be used in lighting systems - The LDR has a high resistance in darkness, triggering the circuit to switch on the light, and it has low resistance in light, triggering the circuit to switch the lights off

How can you use a circuit to measure the resistance of a component?

The component you want to test should be in series with the ammeter and the battery, and the voltmeter should be in parallel across the component - record the current and the voltage, and use V=IR (rearrange to R = V/I) to find the resistance

What are the 2 ways of joining electrical components (2 types of circuits)

In series and in parallel

What is the current through each component in series?

There is the same current through each component

What is the potential difference through each component in series?

The total potential difference of the power supply is shared between the components

What is the resistance of a component in series, and the equation to show this?

The total resistance of all components is the sum of the resistance of each component (Total = R1 + R2)

What is the potential difference across each component in parallel?

The potential difference across each component is the same

What is the current through a component in parallel?

The total current through the whole circuit is the sum of the currents through the separate components

What is the total resistance of a parallel circuit?

The total resistance of two resistors is less than the resistance of the smallest individual resistor.

What are the differences between parallel and series circuits?

Series circuits connect components in a single line, and if 1 component stop working, the whole circuit stops, whereas in a parallel circuit, the components are connected side by side or parallel to each other, and will continue working if a component breaks.

Why does adding resistors in series increase the total resistance?

The total pd is shared between more resistors, so the pd across each resistor is less - the current through the resistors is therefore less, and ass total pd is unchanged, total resistance is greater

Why does adding resistors in parallel decrease the total resistance?

The total pd is the same across each resistor, so adding a resistor increases the total current - because total resistance = battery pd divided by total current, the total resistance is less (more paths for the current to flow)

What the design and use of dc series circuits for measurement and testing purposes?

Different components are connected in a line between a + and - terminal - we can easily change, measure and calculate the pd (voltmeter in parallel), current and resistance, or test components such as lightbulbs or motors, and we can also learn art electricity and how to fix problems

What type of supply (ac or dc) is main electricity?

AC - Alternating current

What is the frequency of electricity the electricity supply in the UK?

50Hz

What is the potential difference of the electricity supply in the UK?

230V

What type of cable is used to connect most electrical appliances to the mains?

Most electrical appliances are connected to the mains using three- core cable.

What is the brown wire?

Live wire

What is the function of the live wire?

The live wire carries the alternating potential difference from the supply.

What is the blue wire?

Neutral wire

What is the function of the neutral wire?

The neutral wire completes the circuit

What is the green and yellow striped wire?

The earth wire

What is the function of the earth wire?

The earth wire is a safety wire to stop the appliance becoming live.

What is the potential difference between the live and earth wire?

About 230V

What is the pd of the earth wire?

0V

What is the pd of the neutral wire?

At, or close to, earth potential - 0V

When is the only time the earth wire carries current?

It only carries a current if there is a fault.

Why should you be careful with the live wire?

A live wire may be dangerous even when a switch in the mains circuit is still open - its pd changes from + to - rapidly - the switch only interrupts flow of current in one part of the circuit - there's still a risk of electric shock

What are the dangers of providing any connection between the live wire and earth?

It creates a complete circuit, and the earth wire has very low resistance, giving a direct path for current to flow to the ground - this mains the appliance could become live and shock you, or fire

What 3 factors is the power transfer in any circuit device related to?

The power transfer in any circuit device is related to the potential difference across it and the current through it, and to the energy changes over time

What is the equation for power using potential difference and current?

Power = pd x current (P = VI)

What is the equation for power using current and resistance?

Power = current^2 x resistance (P = I^2R)

What does the amount of energy an appliance transfers depend on?

How long the appliance is switched on for and the power of the appliance.

How do different appliances transfer energy from batteries or ac mains to the kinetic energy of electric motors?

Fans + washing machines use motors - when you tern them on electricity from the batteries or wall socket (ac mains) power the motor, which then makes parts move, making the appliance work

How do different appliances transfer energy from batteries or ac mains to the energy of heating devices?

Stoves and kettles use heating elements - when you turn them on, electricity from batteries or the wall socket (ac mains) flows through, making the element hot, and that heat cooks or boils

What is done when charge flows in a circuit?

Work is done when charge flows in a circuit.

What is the equation for energy transferred by electrical work using power and time?

Energy transferred = power x time (E = Pt)

What is the equation for energy transferred using charge flow and pd?

Energy transferred = charge flow x pd (E = QV)

How is the power of a circuit device related to the pd across it and the current through it?

The current is the charge flow per second, and the pd is the energy transfer per unit charge - the power is energy transferred by current per second, so power = current x pd (P = IV)

How is the power of a circuit device related to the energy transferred over a given time?

The current through an appliance transfers energy to it from power source - the power of an appliance is energy it transfers in joules per second, so power = energy transferred over time

What's the relationship between the power ratings of appliances and the changes in stored energy?

The power rating of an appliance is related to the rate they consume energy, so appliances with higher power ratings consume energy faster- eg kettles with a high power rating consumes energy at a faster rate

What is the national grid?

The National Grid is a system of cables and transformers linking power stations to consumers

What is used to transfer electrical power from station to consumers?

Electrical power is transferred from power stations to consumers using the National Grid.

What is the purpose of step up transformers?

Step-up transformers are used to increase the potential difference from the power station to the transmission cables t

What is the purpose of step down transformers?

Step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.

Why is the National Grid system is an efficient way to transfer energy?

By making grid pd large, less current is needed to transfer the same amt of power, so there is less power loss due to resistance heating in the cables.

What happens when certain insulating materials are rubbed against each other?

When certain insulating materials are rubbed against each other they become electrically charged.

What is rubbed off when insulating materials are rubbed together?

Negatively charged electrons are rubbed off one material and on to the other.

What charge does the material that gains electrons become?

The material that gains electrons becomes negatively charged.

What charge does the material that lost electrons become?

The material that loses electrons is left with an equal positive charge.

What happens when 2 electrically charged objects r brought close to each other?

They exert a force on each other.

Do 2 objects that carry the same charge attract of repel?

Repel

Do 2 objects that carry different types of charge attract or repel?

Attract

Attraction and repulsion between 2 charged objects is an example of what type of force?

Non contact force

Describe evidence that charged objects exert forces of attraction or repulsion on one another when not in contact.

In 2 charged objects, one creates an electrostatic field, and the other experiences a force inside it - oppositely charges objects near each other experience an attractive force and pull together, whereas like charge objects experience a repulsive force and push apart

Describe the production of static electricity by rubbing surfaces.

When 2 insulating materials rub together, friction causes a transfer of electrons between the surfaces - one material gains electrons to have a negative charge, one loses electrons to have a positive charge - both materials become electrically charged, creating static electricity

Describe the production of a spark by rubbing surfaces.

If 2 objects are oppositely charged, electrons in air molecules r attracted towards the + one - if the field is too strong, there's a spark as some electrons r pulled out of the air and hit other air molecules, knocking electrons out and creating a sudden flow of electrons

Explain how the transfer of electrons between objects can explain the phenomena of static electricity.

When 2 insulating objects rub, they gain opposite electrical charges through electron transfer- bcuz like charges repel, and opposites attract, static electricity is created, where charged objects can attract or repel w out touching

What does a charged object create around itself?

A charged object creates an electric field around itself

Where is the centric field around a charged object strongest?

The electric field is strongest close to the charged object.

What happens to the field the further away from the charged object?

The further away from the charged object, the weaker the field.

What happens to a second charged object placed in an electric field?

A second charged object placed in the field experiences a force.