Topic 3 - Electricity Flashcards by Francis Bacnis

What is the relationship between Voltage and Drift velocity?

Voltage is proportional to Current
Current is proportional to drift velocity
So Voltage is proportional to Drift velocity

Voltage⬆️ = Current⬆️ = Drift velocity⬆️

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What is drift velocity?

Electrons move randomly but tend to move in just one way

The average velocity of the electrons as they flow through the lattice is called the Drift Velocity

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What is the formula for drift velocity?

I=nvqA

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Fluorescent light bulb: What is the Conductor, Charge Carrier and Explanation?

Conductor: Plasma
Charge carrier: Electrons and positive ions
Explanation: Voltage,Potential difference, Gas becomes ionised then turns into plasma so electrons can flow.

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Lightning: What is the Conductor, Charge Carrier and Explanation?

Conductor: The Air
Charge carrier: Electrons and positive ions
Explanation: Electrons build up in base of cloud due to friction, induce positive ions (ionise) on the earth. Electrons connect to the earth through this.

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Filament lamp: What is the Conductor, Charge Carrier and Explanation?

Conductor: Metal (Tungsten) bc of High M.P
Charge carrier: The electron
Explanation: Metals contain free electrons. When energy is supplied, they’re able to move within the lattice.

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What are the 4 states of matter?

Solid, Liquid, Gas, Plasma

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What is the charge of an electron?

1.6x10^-19

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State Kirchoffs’s 1st Law

The sum of the currents leaving any junction is equal to the sum of the currents entering AT THE SAME RATE

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What are the rules for Current, Voltage and Resistance for a Parallel circuit?

Sum of currents in each branch is equal to the current of the power supply.
Voltage is the same at all points in the circuit
(1/Rtotal= 1/R1 + 1/R2 + 1/R3 + …) , The Total resistance is less than the value of the smallest resistor.

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State Kirchoff’s 2nd Law

The sum of the voltages of all of the components is equivalent to the total EMF of the power supply.

The total voltage of all of the components in a closed loop of circuit is equal to the emf of the cell

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What are rules for Current, Voltage and Resistance for a series circuit?

Current is the same at all points
The sum of voltages add up to the voltage of the power supply
(Rtotal= R1+R2+R3 +…) Larger that the value of the largest resistor

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Recall Ohm’s Law

The current in an Ohmic Conductor is directly proportional to the Potential Difference, providing that all physical conditions such as temperature are kept constant.

V=IR

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What is Resistance?

The opposition to the flow of charge. This is measured in ohms.

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How does an increase in temperature lead to an increase in resistance?

An increase in temperature leads to more energy transferred to the metal ions within the lattice
More Energy means a** higher amplitude of oscillation** for the metal ions.
This means that there will be more frequent collisions between the electrons and ions within the lattice
This causes an interference of the flow of charge thus increasing resistance

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What are the factors that affect the resistance of a wire?

The material the wire is made of
The length of the wire
The cross sectional area of the wire

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How does the length of wire affect resistance?

A longer wire means there are** more atoms within the lattice**
This means that there will be** more frequent collisions** between the electrons and ions
The flow of charge is impeded, thus** increasing resistance**

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How does cross sectional area affect resistance?

A larger cross sectional area means there is more space between the atoms and ions within the lattice.
Therefore there will be less frequent collisions between the flow of charge and the ions.
The flow of charge is not impeded, so resistance decreases.

What is resistivity?

A measure of how strongly a material opposes the flow of current. THIS IS NOT RESISTANCE

How does Material affect resistance

What is the relationship between Resistance and resistivity?

Resistance⬆️ = Resitivity⬆️

What is the formula for resistivity?

Resistance must be the subject of the formula:

R=ρL/A

R- Resistance
ρ- Resistivity
L- Length
A- area

What is the relationship between Length and Resistance and Thus Resistivity?

Length⬆️ = Resistance⬆️ = Resistivity⬆️

What is the relationship between Area and Resistance and thus Resistivity?

Area⬆️ = Resistance ⬇️ = Resistivity⬇️

What is the difference between EMF, Voltage and Potential Difference?

* EMF: Battery doing work to transfer energy to electrons * Voltage: Electrical energy supplied to components by electrons themselves * Potential difference: The difference in energy between two points in a circuit.

How do cells/batteries transfer energy

Chemical energy (in bonds of molecules) ➡️ Electrical Energy (Voltage)

How do generators produce a potential difference?

* Kinetic energy * Electromagnetic induction * Induced P.D

What is EMF?

* Stands for electromotive force * EMF is the electrical energy supplied to the circuit per unit of charge

What is the formula for EMF?

ε=E/Q or V=E/Q

What is internal resistance?

The resistance caused by the batteries themselves which results in the generation of heat.

What formula can we use to find the internal resistance

V= -rI + ε (This can be likened to Y=mx+c)

What happens if the axes are switched? (V= -rI + ε)

The gradient of the line will be r instead of -r. The magnitude of the gradient will always be the internal resistance.

What is a Potential Divider?

* A circuit that has the ability to produce an output voltage as a fraction of the input voltage.

What are the purposes of a potential divider?

* To provide a variable potential difference * To enable for a specific PD to be chosen * To split a PD of a powersource between 2 or more components

How does a thermistor work?

* Temp increase = More charge carriers releases * More charge carriers = More current * More current = Less Resistance

What happens to an LDR as light intensity increases?

* Light intensity increase = Resistance Decrease

What does adding a Thermistor do to a Potential Divider circuit?

it makes a temperature sensor like ones used in a thermostat

What does adding an LDR do to a Potential Divider circuit?

it makes a light sensor circuit

What does adding a Variable Resistor do to a Potential Divider circuit?

It makes a pressure sensor

How are electrons arranged in an Atom?

Electrons are arranged in discrete energy levels within an atom.

What happens if they absorb enough energy?

If enough energy is absorbed by an electron, they can either go up one energy level or even leave the atom.

How are atoms arranged in a gas and how does this affect energy levels?

Atoms are spaced randomly and therefore are discrete from one another So the energy levels are discrete.

How are atoms arranged in a Solid and how does this affect energy levels?

Atoms exist in a lattice and are tightly packed so the energy levels overlap.