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p4-electric circuits Flashcards

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1
Q

What charge does a proton have?

A

Positive

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2
Q

What charge does an electron have?

A

negative

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3
Q

what charge does a neutron have?

A

uncharged

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4
Q

What is a charged atom called?

A

an ion

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5
Q

what do uncharged atoms have?

A

equal numbers of electrons and protons

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6
Q

What happens when you rub a polythene rod with a dry cloth?

A

Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod from the cloth. So the polythene rod becomes negatively charged.

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7
Q

What happens when you rub a perspex rod with a dry cloth?

A

Rubbing a perspex rod with a dry cloth transfers electrons from the surface atoms of the rod on to the cloth. So the perspex rod becomes positively charged.

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8
Q

Explain what happens when you rub two insulators?

A

Some insulators become charged when you rub them with another insulator such as a dry cloth. When you rub the insulator, electrons are transferred from one of the materials to the other material.

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9
Q

Why do charged atoms exert a non contact force on each other?

A

Two charged objects exert a non contact force on each other because of their charge. This is because a charged object creates an electric field around itself. A second object in the field experiences a force because of the field. The field, and therefore the force between the two charged objects, becomes stronger as the distance between the objects decreases.

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10
Q

What is the attraction between like and unlike charges?

A

Like charges repel

Unlike charges attract

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11
Q

What is electric current?

A

Electric current is the flow of electric charge. Current will only flow around a complete circuit if there is potential difference.

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12
Q

What is potential difference?

A

Potential difference(voltage) is the driving force that pushes the charge around. Unit of potential difference= volt, V

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13
Q

What is resistance?

A

Resistance is anything in he circuit which slows the flow down. Unit of resistance= ohm,(the weird symbol)

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14
Q

What does the current flowing through a component depend on?

A

The current flowing through a component depends on the potential difference across it and the resistance.
The greater the resistance across a component, the smaller the current that flows through it.

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15
Q

What equation links charge, current and time?

A

The size of the current is the rate of flow of charge. More charge passes around the circuit when a bigger current flows.
Charge(C)=Current(A) X Time(s)
Q=IT

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16
Q

What is current measured in?

A

Amperes(A)

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17
Q

What is charge measured in?

A

coulombs, C

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18
Q

What is time measured in?

A

seconds, s

19
Q

circuit symbols

A

look at mind map about circuit symbols on wall

20
Q

What is the formula linking potential difference, current and resistance?

A 
Potential difference(V)=Current(A) X Resistance(weird symbol)
V=IR
21
Q

info about ohmic conductors?

A

For some components, as the current through them is changed, the resistance of the component changes as well.
The resistance of ohmic conductors(e.g a wire or a resistor) doesn’t change with the current. At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it.
The resistance of some resistors and components does change, e.g a filament lamp or a diode.
When an electric charge flows through a filament lamp, it transfers some energy to the thermal store of the filament, which is designed to heat up. Resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases.
For diodes, the resistance depends on the direction of the current. They will happily let current flow in one direction, but have a very high resistance if it is reversed.

22
Q

What is the formula for calculating resistance?

A

Resistance=potential difference/ current

23
Q

What is Ohm’s law?

A

The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.

24
Q

Why is a wire an ohmic conductor?

A

A wire is called an ohmic conductor because it’s resistance stays constant as the current changes provided it’s temperature is constant.
The gradient of the line depends on the resistance of the resistor. The greater the resistance of the resistor, the less steep the line.

25
Q

What is the required practical about resistance?

A

Resistance can depend on a number of factors. The resistance of a circuit can depend on a number of factors, like whether components are in series or parallel or the length of wire used in circuit. This practical is about investigating the effect of wire length.

26
Q

What does the ammeter do?

A

Measures the current in amps flowing through the test wire.

The ammeter must always be placed in series with whatever you are investigating.

27
Q

What does a voltmeter do?

A

Measures the potential difference(or pd) across the test wire in volts.
The voltmeter must always be placed in parallel around whatever you are investigating.

28
Q

what is the method for required practical for investigating resistance with length of wire?

A
  • Attach a crocodile crip to the wire, level with 0cm on the ruler.
  • Attach the second crocodile clip to the wire, e.g 10cm away from the first clip. Write down the length of the wire between the clips.
  • Close the switch, then record the current through the wire and the pd across it.
  • Open the switch, then move the second crocodile clip, e.g another 10cm along the wire. Close the switch again, then record the new length, current and pd.
  • Repeat this experiment of different lengths of the test wire
  • Use your measurements of current and pd to calculate the resistance for each length of wire.
  • Plot a graph of resistance against wire length and draw a line of best fit. Your graph should be a straight line through the origin- meaning resistance is directly proportional to length- the longer the wire, the greater the resistance.
  • If your graph doesn’t go through the origin, it could be because the first clip isn’t attached exactly at 0cm, so all your length readings are a bit out. This is a systematic error.
29
Q

What does I-V characteristics refer to?

A 
The term I-V characteristics  refers to a graph which shows how the current flowing through a component changes as the potential difference across it is increased. 
Linear components(e.g an ohmic conductor) have an I-V characteristic that's a straight line 
Non-linear components(e.g a filament lamp or diode) have a curved I-V characteristic.
30
Q

Explain the method of the required practical about I-V characteristics?

A

Set up a series circuit.
Begin to vary the variable resistor. This alters the current flowing through the circuit and the potential difference across the component.
Take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. Repeat each reading twice to get an average pd at each current.
Swap over the wires connected to the cell, so the direction of the current is reversed
Plot a graph pf current against voltage for the component.

31
Q

graph of I-V characteristics?

A

look at mind map on the wall

32
Q

What is a LDR?

A

An LDR is a resistor that is dependent on the intensity of light. In bright light, the resistance falls. In darkness, the resistance is highest.
They have lots of applications including automatic night lights, outdoor lighting and burglar detectors

33
Q

What are thermistors?

A

A thermistor is a temperature resistant resistor.
In hot conditions, the resistance drops
In cool conditions, the resistance goes up
Thermistors make useful temperature detectors e.g car engine temperature sensors and electronic thermostats.

34
Q

What are series circuits?

A

In series circuits, the different components are connected in a line, end to end.
If you remove or disconnect one component the circuit is broken and they all stop. This is generally not very handy, and very few things are connected in series.

35
Q

Potential difference in series circuits?

A

There is a bigger potential difference when more cells are in series.
For example, when two batteries of voltage 1.5V are connected in series they supply a total of 3V.
The total potential difference of the supply is shared between the various components. So the potential differnces round a series circuit always add up to the source potential difference;
V total= V1+V2+V3….

36
Q

Current in series circuit?

A

The same current flows through all the components
i1=I2=I3….
The size of the current is determined by the total potential difference of the cells and the total resistance of the circuit. I=V/R

37
Q

Resistance in a series circuit?

A

In a series circuit the total resistance of two components is just the sum of their resistances:
R total= R1+R2
This is because by adding a resistor in series, the two resistors have to share the total potential difference.
The potential difference across each resistor is lower, so the current through each resistor is also lower. In a series circuit, the current is same everywhere so the total current in the circuit is reduced when a resistor is added. This means the total resistance of the circuit increases.
The bigger a components resistance, the bigger its share of the total potential difference.

38
Q

What are parallel circuits?

A

In parallel circuits, each component is separately connected to the energy supply.
If you remove or disconnect one of them, it will hardly affect the others at all. It is useful as you can switch things on and off.
Everyday circuits often include a mixture of series and parallel parts.

39
Q

Potential difference in a parallel circuit?

A

In parallel circuits all components get the full source of pd, so the voltage is the same across all components.
This means that identical bulbs connected in parallel will all be at the same brightness.

40
Q

Current in parallel circuits?

A

In parallel circuits the total current flowing around the circuit is equal to the total of all the currents through the separate components:
In a parallel circuit, there are junctions where the circuit splits or rejoins. The total current going into a junction has to equal the total current leaving it.
If two identical components are connected in parallel then the same current will flow through each component.

41
Q

Resistance in parallel circuits?

A

If you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors.
In parallel, both resistors have the same potential difference across them as the source. This means that the pushing force making the current flow is the same as the source potential difference for each resistor that you add. But by adding another loop, the current has more than one direction to go in. This increases the total current that can flow around the circuit. Using V=IR, an increase in current means a decrease in the total resistance of the circuit.

42
Q

Required practicle about series and parallel circuits:

method on how to investigate resistors in series?

A

First, you will need 4 identical resistors
Then build the circuit using one of the resistors. Make a note of the potential difference of the battery.
Measure the current through the circuit using the ammeter. Use this to calculate the resistance of the circuit using R=V/I
Add another resistor, in series with the first. Again measure the current through the circuit and use this and the potential difference of the battery to calculate the overall resistance of the circuit.
And then repeat these steps when until you have added all your resistors.
Plot a graph of the number of resistors against the total resistance of the circuit.

43
Q

Required practical about series and parallel circuits:

method on how to investigate resistors in parallel?

A

Using the same equitement as before( so it is a fair test) build the same intiial circuit.
Measure the total current through the circuit and calculate the resistance of the circuit using R=V/I
Next, add another resistor in parallel with the first
Measure the total current through the circuit and use this and the potential difference of the battery to calculate the overall resistance of the circuit.
Repeat these steps until you have added all your resistors
Plot a graph of the number of resistors in the circuit against the total resistance.

44
Q

results and graphs for required practical about parallel and series?

A

look at mind map on wall

physics (4 decks)

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