Electricity

What is current?

Current is the rate of flow of negative charge (electrons)

How do electrical circuits work?

How electrical circuits work: ★ Electric current flows from the negative end of the cell to the positive end ✔︎ Electrons are carrying energy from the cell ★ They pass this energy to the components in the circuit e.g. the lamp ★ When the electrons return to the positive end of the cell, they care carrying less energy than when they left the negative end

What is conventional current?

Conventional current is the opposite way electrons heaving ate through a circuit

What is a simple circuit?

A simple circuit is a circuit with only: ★ One battery ★ One switch ★ One device

What is a series circuit?

A series circuit is a circuit that has only one path for the electric current to flow.

What is a parallel circuit?

A parallel circuit has two or more paths for current to flow through.

What is the unit for current?

The unit for current is Amperes (A)

What is amperes often shortened to?

'Ampere' is often shortened to 'amp'

How do we measure current?

We measure current using an ammeter

What unit is charge measured in?

Electrical charge is measured in the coulomb (C)

What is the symbol for charge?

★ Electrical charge has the symbol: Q ⚠︎︎ Make sure this is a capital Q i.e. not 'q'

How much charge is a current of one ampere?

★ A current of one ampere ★ Is the same as one coulomb of charge flowing per second

What is the size of electrical current the same as?

★ The size of the electrical current ★ Is the Ame as the rate of flow of electrical charge

What is the formula for charge?

Q = It Q — Charge (C) I — Current (A) t — Time (s)

What is the symbol for current?

The symbol for current is I

What energy conversions happens in a lamp?

In a lamp, electrical energy becomes: ★ Light energy ★ Thermal energy

Are metals good conductors of electricity?

Yes, metals are good conductors of electricity

Why are metals good conductors of electricity?

★ Delocalised electrons in the metal carry electrical charge through the metal 𐬽 They are good conductor of electricity

Do insulators conduct electricity

No, insulators do not conduct electricity

Why can't insulators conduct electricity?

★ Electrons cannot pass through insulators 𐬽 They cannot conduct electricity

What happens when you rub two insulators together (e.g. cloth and a plastic rod?)

★ When you rub the plastic with the cloth: ➜ Electrons move from the plastic onto the cloth 𐬽 The cloth has a negative charge (since electrons are negative and it has gained electrons) 𐬽 The plastic rod has a positive charge (since it has lost electrons) ⚠︎︎ Protons do not move ✔︎ The positive charge on the plastic rod is equal to the negative charge on the cloth

What is static electricity?

Static electricity is the buildup of charges on an object.

How does a static electricity generator work?

★ Electrons pass from the top plastic roller onto the belt ★ Electrons pas off the belt and are transferred to Earth ★ Top region of the region becomes positively charged ✔︎ The metal dome spreads out the positive charge

How can an aircraft being refuelled dangerous?

When an aircraft is being refuelled: ★ Electrostatic charge can build up as the fuel throws through the refuelling pipe ➜⚠︎︎ This could cause a spark and trigger an explosion

How can the buildup of static electricity during an aircraft being refuelled prevented?

To prevent the buildup of static electricity: ★ Both the truck and the aeroplane are earthed prior to refuelling ➜ This prevents any charges from building up and leading to a spark

Is electrostatic force a contact or non-contact force?

Electrostatic force is a non-contact force

When do electrically-charged objects attract or repel?

★ When there are two like charges: repel ★ When there are two opposite charges: attract

What are the electric field lines for a positively-charged object?

The electric field lines for a positively-charged object are: ★ Pointing away from the object ★ Perpendicular to the surface (normal force)

What are the electric field lines for a negatively-charged object?

The electric field lines for a negatively-charged object are: ★ Pointing towards the object ★ Perpendicular to the surface (normal force)

What is the elation ship between electrostatic repulsion/attraction and distance?

★ The greater the distance ★ The weaker the electrostatic repulsion/attraction

What is the law for current in series circuits?

In series circuits, current is equal everywhere i.e. I₁ = I₂ = I₃ = Iₖ

What is the law for current in parallel circuits?

In parallel circuits, current is shared between the branches i.e. I = I₁ + I₂ + I₃

What is the law for voltage in series circuits?

In series circuits, voltage is shared between the components i.e. V (the voltage of the energy supply) = V₁ + V₂ + V₃

What is the law for voltage in a parallel circuit?

Voltage is the same everywhere in a parallel circuit

Current in parallel circuits

In parallel circuits, current is shared between the branches i.e. I = I₁ + I₂ + I₃ (ΣIₖ)

What is voltage?

Voltage is the pressure that pushes electricity through an electrical circuit

What unit is voltage measured in?

Voltage is measured in volts (V).

What is the symbol for voltage?

The symbol for voltage is V

What does one volt tell us?

1V tells us that 1J of energy is transferred for each coulomb of charge that is moving through the circuit

What is resistance?

Resistance is the opposition of an object to a flow of current through it.

What is the unit for resistance?

The unit for resistance is the Ohm (Ω)

What is the symbol for resistance?

The symbol for resistance is R

How does resistance work in series circuits?

★ In series circuits, total resistance is the sum of the individual resistors ★ R = R₁ + R₂ + R₃ (ΣRₖ)

How does resistance work in parallel circuits?

In parallel circuits, the total resistance is smaller than the smallest single resistor

Why do energy transfers happen in circuit components?

Energy transfers occur at circuit components due to resistance

HOW do energy transfers happen in circuit components?

★ As they move, electron collide with atoms in the metal ➜ Electrical energy is transferred into other forms e.g. thermal

What does resistance tells us?

Resistance tells us the voltage required to drive a current through a component

What is the equation which links: energy/work done, voltage and charge?

E/W = QV E/W — Energy/work done (J) Q — Charge (C) V — Voltage (V)

Why do electrons require energy to go from the positive to the negative terminal?

Electrons require energy to from the positive to the negative terminal to overcome the force of electrostatic attraction

What is Ohm's law?

Ohm's law: V = IR V — Voltage (V) I — Current (A) R — Resistance (Ω)

What is the IV graph for an ohmic resistor? What does it show?

The IV graph for an ohmic resistor is: ★ The current going through the ohmic resistor is directly proportional to the voltage ➜ It shows that the resistance in the resistor is constant ✔︎ This only applies if the temperature remains constant

When is voltage NOT directly proportional to the current in an ohmic resistor?

Current is NOT direct proportional to the current in an ohmic resistor if the temperature doesn't remain constant

What does directly proportional mean?

Directly proportional means the equation will look like y=mx (NOT y=mx+c) as the y-intercept will always be 0.

What does 'filament' mean?

'Filament' means a very fine wire

How do filament lamps work?

When an electric current passes through a filament lamp: ★ The coiled filament gets extremely hot when current passes through it ➜ This causes it glow and give out light

What is the IV graph for a filament lamp?

IV graph for a filament lamp: ★ The current through a filament lamp is NOT directly proportional to the voltage ★ This is because the filament gets hot ➜ Which causes the resistance to increase ★ When the voltage is very high or low, increasing or decreasing the voltage won't change the current by much

Why is voltage NOT directly proportional to current in a filament lamp?

★ In a filament lamp, current is NOT directly proportional to voltage ✔︎ This is because the filament gets hot ➜ At high temperatures, the atoms in the filament vibrate more ➜ The electrons in the current collide more with the atoms 𐬽 More energy is needed to push the current through the filament ➜ Which causes the resistance to increase

What is the equipment in the resistance RP?

Equipment in resistance RP: ★ Battery ★ Ammeter ★ Voltmeter ★ Length of wire

What error often happens in the resistance RP?

A zero error often happens in the resistance RP

What is zero error?

A type of systematic error caused by equipment not being correctly calibrated or 'zeroed'

How can we deal with zero error in the resistance RP?

To deal with zero error in the resistance RP, we mus subtract the zero error from all readings

How is the zero error in the resistance RP caused by equipment?

The equipment in the resistance RP that causes the zero error: ★ It is difficult to get the crocodile clip exactly at 0 ★ There. Is some resistance caused by the contact between the crocodile clip and the wire

How does heating effects cause problems with the resistance RP?

Ways heating effects causes problems with the resistance RP: ★ If the temperature of the wire increases ➜ The resistance will also increase ➜ This will influence our results

How can we limit the problem of heating effects in the resistance RP?

How we can limit the problem of heating effects in the resistance RP: ★ Use a low voltage ➜ This will keep the current low ➜ Which will reduce any heating in the wire ★ Only turn on the current when taking a reading and turn it off between readings ➜ This will reduce the current ➜ Which will reduce heating in the wire

How does a variable resistor work?

★ A variable resistor contains: ★ A long piece of wire ★ A coil ★ Using the slider, you can change the length of the wire that the current runs through ➜ This changes the resistance

How does an LDR work?

LDR works by: as light intensity increases, resistance decreases

What is the graph for an LDR?

LDR graph: ★ X-axis: light intensity ★ Y-axis: Resistance Brightness Increases Resistance Decreases

How does a phone's screen turn off during conversations (when it is near your ear)?

How a phone's screen turns off during conversations using an LDR (simplified): When the phone is exposed to sunlight: ★ The resistance in the LDR is very low ➜ Because of Ohm's law, the voltage of the LDR is also very low ➜ Because voltage is shared across the battery in series, the voltage of the lamp is high 𐬽 It emits (a lot of) light When the phone is not exposed to sunlight: ★ The resistance in the LDR is rises sharply ➜ Because of Ohm's law, the voltage of the LDR is also very high ➜ Because voltage is shared across the battery in series, the voltage of the lamp is low 𐬽 It emits very low light

How do street lamps work?

Street lamps work by using an LDR

How does a thermistor work?

A thermistor works by having lower resistance when the temperature increases

What is the graph of a thermistor?

The graph of a thermistor is: Temperature Up Resistance Down

How do computer cooling fans work?

How computer cooling fans work using a thermistor: When temperature is high: ★ The resistance in the thermistor is very low ➜ Because of Ohm's law, the voltage of the thermistor is also very low ➜ Because voltage is shared across the battery in series, the voltage of the cooling fans is high 𐬽 The fan switches on (in high power) When temperature is low: ★ The resistance in the thermistor is rises sharply ➜ Because of Ohm's law, the voltage of the thermistor is also very high ➜ Because voltage is shared across the battery in series, the voltage of the cooling fan is low 𐬽 The cooling fan doesn't turn on

How do incubators for premature babies work?

★ Premature babies need to be kept warm ✔︎ The incubator has a system to detect faults ★ If the temperature falls ➜ This is sensed by a resistor ➜ This causes a lamp to turn on and an alarm to sound

What is power?

Power is the rate at which energy is transferred

What unit is power measured in?

Power is measured in watts (W)

What equation links power, energy and time?

Equation that links power, energy and time: P = E/t ★ P — Power (W) ★ E — Energy (J) ★ t — Time (s)

What equation links power, voltage and current?

Equation links power, voltage and current: P = IV ★ P — Power (W) ★ I — Current (A) ★ V — Voltage (V)

What equation links power, resistance and current? How do you obtain this equation?

Equation links power, resistance and current (combining Ohm's law and P=IV): P = IR² ★ P — Power (W) ★ I — Current (A) ★ R — Resistance (Ω)

What equation links power, resistance and coltage? How do you obtain this equation?

Equation links power, resistance and current (combining Ohm's law and P=IV): P = V²/R ★ P — Power (W) ★ V — Voltage (V) ★ R — Resistance (Ω)

How and why do diodes work?

★ In diodes, current flows in one direction only ✔︎ This is because it has a very high resistance in the reverse direction

How do know what direction current flows in a circuit?

We know which direction current flows in a circuit by the direction of the arrow in the diode in the circuit diagram

What are diodes useful for?

Diodes are extremely useful for controlling the flow of current in circuits

What is an LED?

★ An LED (light-emitting diode) gives off light when a current flows through ✔︎ LEDs are an extremely energy-efficient source of light

What are some uses of LEDs?

Uses of LEDs: ★ Flash on a phone camera ★ LED light bulbs ★ LED televisions

Why de switch the direction of the battery in the IV RP?

We switch the direction of the battery in the IV RP to record negative voltages

Why should we not leave the circuit connected for too long for an ohmic resistor in the IV RP?

If we leave the circuit connected for too long in the IV RP: ★ The the temperature of the ohmic resistor will crease ➜ The graph will no longer be a straight line through the origin

Why do you add an extra resistor for the diode IV RP?

★ We add an extra resistor for the diode IV because diodes very easily damaged by a high current ✔︎ The extra resistor will keep the current relatively low ➜ Which will protect the diode

What is a milliammeter?

A milliammeter is a very sensitive ammeter

What type of ammeter do we need in the diode IV RP? Why?

★ In the diode IV RP, we need to use a milliammeter to detect sensitive changes in current ✔︎ This is because the current will be very low

What is the IV graph for a diode?

IV graph for a diode: ★ Voltage < 0.6V: Very low current ✔︎ Because of high resistance ★ Voltage > 0.6V: The current starts rising sharply

What is direct current (DC)?

Direct current is current that flows in only one direction

What is alternating current (AC)?

Alternating current is when electricity flows in alternate directions back and forth in a circuit.

What type of electricity is mains electricity in the UK?

Mains electricity in the UK is alternating current

What is the benefit of alternating current (AC)?

Benefit of alternating current (AC): It is very easy to use a transformer to increase or decrease the potential difference

What is the frequency of alternating current (AC) in the UK?

The frequency of alternating current (AC) in the UK is 50Hz

What is the voltage of alternating current (AC) in the UK?

The voltage of alternating current (AC) in the UK is 230V

What can an oscilloscope be used to measure?

Oscilloscope can be used to measure: ★ Voltage ★ Frequency

How do you measure the voltage in an oscilloscope?

To measure the voltage in an oscilloscope, just measure the voltage at the peak of the wave

How do you measure the frequency in an oscilloscope?

To measure the frequency in an oscilloscope, just measure how long it takes for the wave to repeat (and then do 1/ANS)

What is the formula for frequency?

Formula for frequency is: frequency = 1/[time period]