P3.2 Flashcards
What is voltage
Voltage is a measure of the energy carried by the current (per coulomb of charge)
What is potential difference
Potential difference (P.D) is the difference in (Potential Energy) voltage between two points.
OR
Potential difference is a measure of thework done per coulomb of charge.
Potential difference formula
What does the potential difference across a component indicate
how much energy was transferred by the current as it passed through the component.
What component measures potential difference
Voltmeter
What is resistance
Resistance is the opposition to the passage of charge.
Where does resistance come from
In a wire/component, ions vibrate up and down.These vibrating ions will get in the way of the passing electrons, stopping them from flowing… reducing the current.The faster the ions vibrate (the hotter the wire) or the bigger the ions, the greater the resistance encountered, and the smaller the current flowing.
The higher the resistance…
the more energy transferred by the current as it passes through the resistance.
Resistance formula
What is a series circuit
is one in which the charge must travel through every component.
Has no branches = all one loop
Current in a series circuit
The current through every component in a series circuit is the same.
Resistance in a series circuit
The total resistance in a series circuit is the sum of all the component resistances.
Potential difference in a series circuit
The p.d. across components in a series circuit is shared out…… the greater the resistance of the component…… the greater the share of the total p.d. it has across it.
What is a parallel circuit
A parallel circuit is one in which the charge doesn’t travel through the same components.
HAS BRANCHES
Potential difference in a parallel circuit
The p.d. across components in a parallel circuit is the same.
Resistance in a parallel circuit
The total resistance in a parallel circuit isNOT THE SUM of all the component resistances.(less than smallest resistance in circuit; don’t have to know how to calculate at GCSE)
Current in a parallel circuit
The current in a parallel circuit is split between components/branches.
… the greater the resistance of the component…… the less current through it.
What does the gradient of an IV graph represent
1
—
R
The gradient of an I-V graph is 𝐈/𝐕… this is the reciprocal of 𝐕/𝐈.
A steep gradient on an IV graph means…
Small resistant
A shallow gradient on an IV graph means
Large resistance
What is ohms law
The current through a component is directly proportional to the potential difference across it, as long as the temperature is kept constant.
What does a variable resistor do
Varies CURRENT
As the potential difference increases across a component…
The component gets hotter
Fixed resistor IV graph
What are wires/fixed resistors also known as
Ohmic conductors
Filament light bulb IV graph
Describe + explain the IV graph for a filament light bulb
As P.d increases, increase the current
More current in the filament lamp heats the positive ions
Ions vibrate faster and this opposes the transfer of charge in the filament lamp
Resistance increases
Diode IV graph
What are thermistors
Thermistors are components (resistors) whoseresistance depends upon temperature.
Resistance in thermistors
Resistance decreases as the temperature increases.
OPPOSITE TO NORMAL
Why don’t thermistors behave like regular components ie. Why is their resistance trend opposite
due to the fact they are made of a special type of material, semiconductors.
How does a thermistor work
As you heat a thermistor/semiconductor…
Ions vibrate faster – fewer electrons move through the wire per unit time.(the only thing that happens inside regular components)
More electrons are liberated from atoms of the semiconductor – more electrons move through the wire per unit time.(this effect is more pronounced than #1, so current increases, effectively meaning resistance must have decreased).
What is an LDR
LDRs (light dependent resistors) are components (resistors) whose resistance depends upon light intensity.
Resistance in LDRs
Resistance decreases as the light intensity increases.
OPPOSITE TO NORMAL
How does LDRs work
As you give an LDR/semiconductor morelight energy…
Ions vibrate faster – fewer electrons move through the wire per unit time.(the only thing that happens inside regular components)
More electrons are liberated from atoms of the semiconductor – more electrons move through the wire per unit time.(this effect is more pronounced than #1, so current increases, effectively meaning resistance must have decreased).
Suggest why the graphs of resistance against temperature, and of resistance against light level, eventually level off.
Resistance in thermistors and LDRs is primarily determined by the number of free electrons.
Increasing temperature and levels of light increase the number of free electrons.
Eventually after a certain amount of heat/light energy, all electrons will have been liberated, and resistance will no longer change with increasing temperature/light.
If you add more resistors to a parallel circuit, what happens to the net resistance
Decreases
How do sensor circuits work
- A fixed resistor of resistance R1 is connected in series with a thermistor of resistance R2.
- The p.d. of the battery is shared out amongst the fixed resistor and the thermistor(most dropped across highest resistance)
- The thermistor is connected in parallel with a component (eg – heater), the p.d. across both is VOUT.
- As the temperature in house decreases,resistance of thermistor, R2 increases.
- The p.d. dropped across the thermistor,VOUT, increases.
- Once VOUT increases to a high enough level,the “working potential” of the heater is reached and it switches on.
Power Formula
What is power
The rate of energy transfer
Electrical power formula
Electrical power formula - if you don’t know voltage (V)
What is DC
A current that is steady, constantly flowing in the same direction in a circuit, from positive to negative
What is AC
A current that continuously changes its direction, going back and forth around a circuit
Frequency of AC
number of times the current changes direction back and forth each second
Graph of DC
Graph of DC
Comparing AC & DC
Define electric field
A region where an electric charge experiences a force
Insulators vs conductors
Conductors allow charge carriers to freely move. Insulators do not allow charge carriers to move.
Good conductors
Good insulators
Two types of thermistors
NTC and PTC
What is NTC
negative temperature coefficient - have a lower resistance when the temperature increases
What is PTC
positive temperature coefficient - thermistors have a higher resistance when the temperature increases
