p2 - electricity

What is current a measure of?

Current is a measure of the rate of charge in a circuit, indicating how fast charged particles travel.

How is current measured?

Current is measured in Amperes (A).

What device is used to measure current?

An ammeter is used to measure current and must be placed in series.

How do you convert from milliAmperes to Amperes?

To convert mA to A, divide by 1000.

What is the unit of resistance?

Resistance is measured in Ohms (Ω).

What is potential difference also known as?

Potential difference is also known as voltage.

What does potential difference do?

Potential difference is the driving force that makes current travel, measured in volts (V)

What device is used to measure voltage?

A voltmeter is used to measure voltage and must be placed in parallel.

What is the equation for charge flow?

The equation for charge flow is Q = I x T.

What does Q stand for in the equation Q = I x T?

Q stands for charge flow measured in coulombs (C).

What is Ohm's Law?

Ohm's Law is expressed as V = I x R.

What happens to current when resistance increases?

When resistance increases, current decreases - resistance slows the flow

What is the effect of wire length on resistance and what is the method?

As the length of the wire increases, resistance also increased, should be directly proportional

how does increased current effect resistance?

as current increases so does resistance, this is because the electrons are flowing through quicker and with more energy, some of the energy is transferred is to metal atoms in the wire causing them to vibrate more, making it harder for the electrons to flow through which causes RESISTANCE

What is a light-dependent resistor (LDR)?

An LDR is a resistor whose resistance depends on light intensity.

What happens to an LDR when light intensity is high and what can they be used in?

When light intensity is high, the resistance of an LDR decreases, in darkness, resistance increases, they can be used in outdoor lighting, automatic night lights and burgler detectirs

What is the function of a thermistior and can they be used in?

A thermistor increases its resistance when it’s cold and decreases its resistance when it’s hot, can be used in temp detectors in cars and electronic thermostats

What is true about series circuits when one component is removed?

Removing one component from a series circuit breaks the entire circuit, making them less useful

What happens to potential difference in a series circuit?

Potential difference is shared among the components in a series circuit, the p.d at each component will always add up to equal the source p.d

What is the relationship of current and resistance in a series circuit?

Current is determined by the total potential difference and total resistance, I = V / R

What is the advantage of using parallel circuits?

If one component is removed, the circuit remains functional.

What is the potential difference across all components in a parallel circuit - what does this mean for bulbs?

The potential difference is the same across all components in a parallel circuit, 2 identical bulbs will always burn at the same brightness

How does adding resistors in parallel affect total resistance and what is the rule you ALWAYS FORGET.

Adding resistors in parallel decreases total resistance, the total resistance is always smaller than the resistance of the smallest of the 2 resistors, as there are more places for the current to go

why do power stations operate below maximum power output?

Power stations usually operate below their maximum power output to handle increased demand.

What is the maximum mains voltage supply in the UK?

The maximum mains voltage supply in the UK is 230 volts at a frequency of 50 Hz

What type of current is used in batteries?

Batteries supply direct current (DC), it only flows in one direction

What equations calculate power?

Power can be calculated using P = V x I and P = I squared x V if you don’t know potential difference

What is the equation for efiiciency?

Efficiency is useful output energy transfer divided by total input energy transfer.

What is a step-up transformer?

A step-up transformer increases potential difference and decreases current - it takes more turns on the secondary coil

How does a step-down transformer function?

A step-down transformer decreases potential difference and increases current - it takes more turns on the primary coil

What is the efficiency of transformers?

Transformers are nearly 100% efficient, meaning power in the primary coil equals power in the secondary coil.

What is the rule for current in parallel circuits?

current is shared between branches, if 2 identical components are joined in paralell, the same current will flow through them

What is the rule for current in a series circuit?

Current is the same everywhere

What is the rule for resistance in a series circuit?

Resistance adds up in a series circuit, the bigger a components resistance, the bigger its share of potential difference

What happens to cell potential difference in a series circuit?

it adds up,m adding cells increases p.d when they’re connected in series

describe the relationship between current and resistance in an ohmic conductor like a wire AT A CONSTANT TEMP and explain why

directly proportional, as the current increases so does the resistance (due to thermal energy being lost as the wire heats up)

explain how a thermistor can be used in a sensing circuit for a fan

• thermistors inc/dec resistance based on temperature

• a circuit should be built, with a fixed resistor in a loop with the fan motor and a thermistor in series with the fixed resistor

• the fan motor and the fixed resistor will have the same p.d, as they’re connected in parallel

• the p.d is shared out between the loop and the thermistor according to their resistances, the bigger resistance a component has the more p.d it takes

• as the room gets hotter, the thermistors resistence decreases, leaving a bigger share of p.d for the loop, which supplys more energy to the fan motor making it spin when the room is hot!

explain the relationship between current and resistance in a filament lamp

as the current increases, the temp of the filament increases, so the resistance increases

explain the relationship between current and resistance for a diode

diodes only allow current to flow one way, if the current tries to flow in the reverse direction, resistance is very high