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Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

What must have a circuit have in order for current to flow?

A

Must be complete and have a source PD.

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2
Q

What is current and what is it due to?

A

It is the rate of flow of charge I=Q/t and it is due to the passage of charged particles called charge carriers

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3
Q

What are the charge carriers in a Metal and what do they do?

A

They are conduction electrons move around and they repeatedly collide with each other and the fixed positive ions in the metal.

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4
Q

How can you display conduction?

A

Battery ammeter and material required.Connect them.Battery forces the charge carriers through the conducting material.Electrons enter the battery at the positive terminal and flow out of the negative terminal to the rest of the circuit.

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5
Q

Conventional flow, formula and unit of current?

A

+ to -,Q=it and ampere 1 C/s

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6
Q

Arrangement of electrons in Insulator?

A

Each electron is fixed to an atom in the material and cannot move.When a voltage is applied across the material no current flows as electrons cannot pass through the material.

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7
Q

Arrangement of electrons in conductor?

A

Most of the electrons are attached to atoms, there are delocalised electrons that are attracted to the positive terminal of the metal when a voltage is applied across the material.

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8
Q

Arrangement of charge carries in semiconductor?

A

The number of charge carriers increase with temperature so resistance decreases with temperature.Pure semiconductors called intrinsic semiconductors conduction is due to electrons that break free from these atoms.

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9
Q

Electron flow through a filament lamp?

A

Bulb connected to battery receives a fixed amount of energy from the electrons that flow through it.Electrons take a fixed amount of energy from the battery and transfer it to the filament lamp.Then they enter the battery from the positive terminal and repeat this process.

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10
Q

What do electrons have to do to pass through a component?

A

When a battery is in a circuit, electrons have to do work to pass through circuit components.In this process they transfer most if not all of their energy. Therefore work done=loss energy.

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11
Q

What is voltage?

A

Voltage is the work done per unit charge.V=W/Q 1volt=1J/C

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12
Q

What is EMF?

A

The electrical energy produced per unit of charge passing through a source. Electrical energy=Qx emf

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13
Q

What happens when current flows through a component with resistance in it?

A

When current flows through the component it makes it heat up.This is because the charge carriers repeatedly collide with the atoms of the material transferring energy to them making them vibrate more which heats the component.Work done on the device is transferred as thermal energy.

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14
Q

Whats the formula for energy transferred?

A

E=IxVxT P=e/t

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15
Q

What is resistance and what is it caused by?

A

Resistance opposes the flow of charge.Resistance is caused by the charge carriers colliding with each other and the fixed positive ions of a conductor.V=IR

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16
Q

What is Ohms law?

A

It states that the Voltage across a metallic conductor is directly proportional to the current across the conductor provided the physical conditions don’t change.

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17
Q

How to measure the resistance of a resistor?

A

Connect battery variable resistor ammeter voltmeter and resistor.Use the variable resistor to vary the current and voltage.Record the variations of the voltage and current.Plot a graph of V against I.The gradient of the graph is the resistance.

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18
Q

What is resistivity?

A

Resistivity is the extent to which the material opposes the flow of charge. Resistivity =RA/L.Unit ohm/m

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19
Q

How to measure the resistivity of a wire?

A

Battery Ammeter Wire Length Flying lead Voltmeter and length.Measure diameter of wire in at-least 3 positions using micrometer.Calculate the cross sectional area of the wire using piD^2/4.Vary the length of the wire and measure the voltmeter and ammeter readings for each length.Calculate the resistance at each length using V=IR.Plot a graph of R against L. Gradient equals Restivity/Area multiply by area to get value for resistivity..Keep temp constant.

20
Q

Describe a superconductor and where r they used?

A

A superconductor is made of a. material that has zero resistivity at and below the critical temperature depending on the material.When a current passes through the material there is zero Pd and zero resistance .There is no heating effect.They are used in electrical energy wires so no energy is lost.High powered electromagnets.Transition temperature converts materials to superconductors.

21
Q

What diodes?

A

Electrical device which only allows current to flow in a single direction called the forward direction.About 0.6v threshold voltage to conduct.Very small current in reverse direction.

22
Q

Properties of thermistors?

A

Increase in temp increases current but reduces resistance for an intrinsic semiconductor like silicon.Negative temp coefficient.Intrinsic semiconductor as number of charge carries increases with temperature.

23
Q

Properties of LDR?

A

Increase in light intensity increases current but reduces resistance.

24
Q

What can u do with a potential divider?

A

U can vary the current to zero whereas with a variable resistor you cant.

25
Q

What happens to the resistance of a metal as the temperature rises?

A

It increases with temperature.This is because the fixed positive ions vibrate more making it more difficult for conduction electrons to pass through the metal when a pd is applied.

26
Q

Kirchoffs law?

A

The current entering a junction=current leaving the junction.For any complete loop of a circuit the sum of potential drops across the loop equals the sum of emfs around the loop.

27
Q

What happens when charge carriers lose and gain energy?

A

Potential drop and potential rises equal to the pad across the battery as charge carriers gain energy.

28
Q

Emf and potential drops definitions?

A

Total electrical energy produced per coulomb in a loop=the total electrical energy per coulomb transferred around the loop.

29
Q

Total resistance in series and parallel formulas?

A

R1+R2=R 1/r2+1/r2=1/r

30
Q

Heating effect of a current?

A

Due to resistance of component.Charge carriers repeatedly collide with the positive ions of the metal transferring energy to them.Making them vibrate and heat up.Once the KE of the charge carriers is lost the pd provides a force accelerating the charge carriers until they collide with another positive ions.Net transfer of energy by charge carriers to atoms

31
Q

Formulas for power

A

p=iv p=V^2/r p=I^2r P=E/T P=I^2rt

32
Q

What is internal resistance?

A

A sources opposition to the flow of charge through it.Defined as the pd lost per unit current passing through the source.

33
Q

Formula for EMF

A

E=Energy/Charge.

34
Q

What is the EMF of the terminal pd?

A

The pd across the terminals of the source is the electrical energy per unit of charge delivered by the source when in the circuit.The terminal pd is less than the emf whenever current passes through the source due to internal resistance.

35
Q

EMF formula

A

Emf=Terminal pd + lost volts.E=IR+ir

36
Q

When is max power delivered to a load?

A

When load resistance=internal resistance

37
Q

Calculate EMF of a source?

A

Voltmeter across battery ammeter variable resistor and lamp.Current is changed by varying the variable resistor.Lamp limits the max current that can pass through the cell.Ammeter measures cell current.Terminal pd against current should be plotted.Gradient gives internal resistance.Terminal pd reduces as current increases.Straight line with negative gradient.V=Emf-Ir

38
Q

How to calculate emf?What is net emf in same direction.

A

EMF=cell current x total resistance.Addition in same direction subtraction in opposite.

39
Q

How to find voltage of a group of cells?

A

V=emf-Ir/n

40
Q

Whats the pd of a diode.

A

Em in reverse direction

41
Q

What is a potential divider?

A

Two or more resistors that are in series with each other and a source of fixed pd.The pd is divided by the components.

42
Q

What can a potential divider be used for?

A

Can be used to supply a fixed pd between 0 and source pd.

43
Q

What does a sensor circuit do?

A

A sensor circuit produces an output pd that changes due to a change in a physical condition such as temp or light intensity.

44
Q

What does a temp sensor consist of?

A

Consists of a potential divider made from a thermistor and variable resistor.With temp of thermistor constant the source pd can be divided between the source pd and variable resistor.The potential divider can be adjusted to give the thermistor a desired value.However,if the temp rises the resistance and pd through the thermistor falls.

45
Q

Describe the shape of a filament lamp?

A

Low voltage obeys ohms law.As current increases resistance increases and filament lamp gets hotter so gradient reduces

Physics (19 decks)

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