p4-electric circuits

Question 1

What charge does a proton have?

Answer 1

Positive

Question 2

What charge does an electron have?

Answer 2

negative

Question 3

what charge does a neutron have?

Answer 3

uncharged

Question 4

What is a charged atom called?

Answer 4

an ion

Question 5

what do uncharged atoms have?

Answer 5

equal numbers of electrons and protons

Question 6

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

Answer 6

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.

Question 7

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

Answer 7

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.

Question 8

Explain what happens when you rub two insulators?

Answer 8

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.

Question 9

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

Answer 9

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.

Question 10

What is the attraction between like and unlike charges?

Answer 10

Like charges repel

Unlike charges attract

Question 11

What is electric current?

Answer 11

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

Question 12

What is potential difference?

Answer 12

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

Question 13

What is resistance?

Answer 13

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

Question 14

What does the current flowing through a component depend on?

Answer 14

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.

Question 15

What equation links charge, current and time?

Answer 15

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

Question 16

What is current measured in?

Answer 16

Amperes(A)

Question 17

What is charge measured in?

Answer 17

coulombs, C

Question 18

What is time measured in?

Answer 18

seconds, s

Question 19

circuit symbols

Answer 19

look at mind map about circuit symbols on wall

Question 20

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

Answer 20

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

Question 21

info about ohmic conductors?

Answer 21

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.

Question 22

What is the formula for calculating resistance?

Answer 22

Resistance=potential difference/ current

Question 23

What is Ohm’s law?

Answer 23

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

Question 24

Why is a wire an ohmic conductor?

Answer 24

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.

Question 25

What is the required practical about resistance?

Answer 25

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.

Question 26

What does the ammeter do?

Answer 26

Measures the current in amps flowing through the test wire. | The ammeter must always be placed in series with whatever you are investigating.

Question 27

What does a voltmeter do?

Answer 27

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.

Question 28

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

Answer 28

- 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.

Question 29

What does I-V characteristics refer to?

Answer 29

``` 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. ```

Question 30

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

Answer 30

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.

Question 31

graph of I-V characteristics?

Answer 31

look at mind map on the wall

Question 32

What is a LDR?

Answer 32

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

Question 33

What are thermistors?

Answer 33

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.

Question 34

What are series circuits?

Answer 34

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.

Question 35

Potential difference in series circuits?

Answer 35

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....

Question 36

Current in series circuit?

Answer 36

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

Question 37

Resistance in a series circuit?

Answer 37

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.

Question 38

What are parallel circuits?

Answer 38

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.

Question 39

Potential difference in a parallel circuit?

Answer 39

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.

Question 40

Current in parallel circuits?

Answer 40

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.

Question 41

Resistance in parallel circuits?

Answer 41

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.

Question 42

Required practicle about series and parallel circuits: | method on how to investigate resistors in series?

Answer 42

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.

Question 43

Required practical about series and parallel circuits: | method on how to investigate resistors in parallel?

Answer 43

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.

Question 44

results and graphs for required practical about parallel and series?

Answer 44

look at mind map on wall