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Electricity Flashcards

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1
Q

What is static electricity

A

The build up of charge on an insulator. One method that we can use to build up charge on an insulator is charging by friction

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2
Q

What is charging by friction

A

Where electrons are moved from one object to another by applying a frictional force. The electrons move as they have a much lower mass and are in the outer shell so aren’t as tightly bound.

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3
Q

How does a insulator become negatively charged when rubbed with a dry cloth

A

The frictional force has moved the electrons from the cloth to the rod. The insulator does not lose its charge as the electrons are not delocalised.

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4
Q

what happens when two objects have the same charge

A

they repel

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5
Q

what happens when two objects have different charges

A

they attract

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6
Q

what is charging by induction

A

a method to charge a neutral object by bringing a charged object nearby (without touching). and causing the electrons to redistribute within the neutral object.

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7
Q

What happens when a negatively charged balloon is brought next to a neutral wall

A

-Negative charges on the balloon attract the positive charges on the wall. the negative electrons in the wall repel slightly away from the surface of the wall. This causes an induced positive surface attraction

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8
Q

What happens when a charged polythene rod is brought close to the cap of an electroscope but they do not make contact.

A

-the gold leaf rises
-the electrons in the metal are repelled by the negatively charged polythene rod
-so the electrons are pushed from the rod to the leaf and move away from the negative rod
-no transfer of electrons

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9
Q

What happens when an electroscope is charged by direct contact with a charged Perspex rod (positive)

A

-the gold leaf rises
-the positively charged rod attracts the negatively charged electrons in the metal and they transfer when they come into contact and are rubbed together
-this means that the rod and the metal leaf have a slightly positive charge so they repel

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10
Q

what are some materials that are electrical conductors

A

metals e.g copper, silver, gold

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11
Q

what are some materials that are insulators

A

rubber, plastic, glass

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12
Q

what is a danger of electrostatic charges

A

when fuelling aircrafts and tankers

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13
Q

how is earthing wire used to protect airport workers when refuelling a plane

A

-the plane is earther using a conductor (eg earthing wire) as soon as it lands, before refuelling begins
-this allows the charge that has built up to flow through to the earth
-this prevents sparks which could cause an explosion

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14
Q

why is there a build up of charge during the refuelling process of an airplane

A

As the aircraft flies through the air, friction causes them to become charged with static electricity. After the aircraft has landed there is a possibility of charges escaping to the earth as a spark so it must be earthed. The same happens to a car after a long journey as the fuel tankers can become charged.

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15
Q

How does an inkjet printer work using static electricity

A

Each spot of ink is given a charge so when it is sprayed onto the paper, it falls between a pair of directing plates and electrostatic forces direct it to the correct position. The charges on the plates change hundreds of times each second so each drop fall in a different position forming pictures pictures and words.

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16
Q

How does a photocopier work with static electricity

A

positive charges are sprayed onto a turning drum whose surface is covered with a metal called selenium. A bright light is shone onto the paper to be copied. The white parts of the paper reflect light onto the drum and the dark/printed parts do not. In the places where light is reflected, the selenium loses charge but where it is dark, the charge remains. A negatively charged carbon powder called toner is blown across the drum and sticks to the parts which are charged. A sheet of paper is then pressed against the drum and picks up the pattern of carbon powder. The powder is then fixed in place with a heater forming words and pictures.

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17
Q

What is a current

A

the rate of the flow of charge

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18
Q

what is the voltage/potential difference

A

the energy transferred per unit charge

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19
Q

What is the link between current charge and time

A

charge= current X time or Q=I x t

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20
Q

What is the relationship between charge, voltage and energy transferred

A

energy transferred= charge x voltage or E= Q x V

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21
Q

what is voltage measured in

A

volts, V

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22
Q

What is current measured in

A

amps, A

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23
Q

what is charge measured in

A

coulombs, C

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24
Q

what is time measured in

A

seconds, S

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25
what is energy transferred measured in
Joules, J
26
what is ohms law
the potential difference is proportional to the current for a component with fixed resistance. (Current is inversely proportional to resistance)
27
what is the relationship between voltage, current and resistance
voltage = current x resistance or V= I x R
28
what is resistance measured in
ohms, lululemon symbol
29
what factors affect resistance
-length of wire: increases resistance as the longer the wire, the more positive ions exist. This means there are more opportunities for collisions between electrons and ions This reduces the current and increases resistance -temperature increase: resistance increases due to ion vibration and more collisions -cross sectional area increases: resistance decreases as there are more possible routes material choices change resistance (resistivity)
30
what is the qualitative effect of changing resistance on current in a circuit
if resistance increases current decreases and is resistance decreases, current increases/ This happens if the voltage remains constant
31
how does current vary with voltage in a wire/resistor
-directly proportional relationship -linear relationship -pattern statement -constant fixed resistance so V=I x R -gradient of voltage and current graph of a wire gives resistance e.g R -gradient of current and voltage graph gives inverse of resistance e.g 1/R
32
draw a resistor graph with voltage and current
33
draw a bulb (filament lamp) graph with current and voltage
34
DESCRIBE how does resistance vary in a bulb (filament lamp)
as the voltage increases, the resistance increases
35
EXPLAIN how resistance varies in a bulb (filament lamp)
as the voltage increases, more energy is delivered to the ions in the filament. The bulbs temperature increases and ions vibrate more. This increases collisions between ions and electrons making it more difficult for current to flow. Therefore, resistance increases
36
where is the low and high resistance on a bulb (filament lamp) graph
where the gradient is shallower, there is a higher resistance and where the gradient is steeper there is a lower resistance
37
how do you find the gradient on a bulb (filament lamp) graph
go up from the voltage to the line and across from the current. Then do V=I x R or do current/ voltage which gives the inverse of the resistance and then flip it around 🦹‍♀️
38
what can be inferred if there is a straight line on a blub (filament lamp) graph
-going from bright to dim mitigates temp change -if the experiment is done too quick there is no temp change
39
Draw a diode graph of current and voltage
40
How does resistance vary in a diode
-in forward bias there is a low resistance so current flows -in a reverse bias there is a very high resistance so no current flows
41
how do you draw a diode symbol in a circuit
if the arrow points right, current flows as the diode is in forward bias. If the arrow faces left, no current flows and the diode is in reverse bias. This happens when the charge flows from positive to negative
42
how does the current in a series circuit depend on the applied voltage
voltage and current are directly proportional so if voltage increases current increases -current and resistance are inversely proportional so if one increases, the other decreases
43
what is the relationship between energy transferred, current, voltage and time
Energy transferred= current x voltages x time or E = I x V x t
44
what is the relationship between power, current and voltage
power = current x voltage or P = I x V
45
When are LDR's used (light dependant resistors)
lampposts, automatic lighting
46
draw a LDR graph with resistance and light intensity
47
What is the relationship between resistance and light intensity in a LDR
-As the light intensity increases, the resistance decreases -inversely proportional relationship -non linear
48
what is an example of a semi conducting material
silicon
49
where would we use thermistors
fridges, kettles, ovens. computers, phones, radiators/thermostats
50
what is the relationship between resistance and temperature in a thermistor
-as the temperature increases, resistance decreases -non linear -inversely proportional
51
How do you know whether the current is flowing through a LED or a bulb
the bulb will light up
52
what is the electrical current in solid metallic conductors
a flow of negatively charged electrons
53
What happens when fine powder charged by friction comes into contact with an electroscope
-the thin piece of metal rises as it repels the metal rod -if the powder will have a negative charge -the metal can, cap, rod and thin piece of metal are conductors which allows the electrons to be transferred through the metal -the electrons are transferred into the metal rod and the thin piece of metal -as all the pieces of metal have the same charge they repel and the thin piece of metal rises
54
What happens when a electroscope is charged by direct contact with a charged polythene rod (negative)
-gold leaf rises -the electrons pass into the electroscope and spread out -the metal rod and gold leaf are now both negative so they repel
55
Do circuit symbols flashcards
56
Label a plug diagram
🤥
57
What are the seven main parts of a plug
-earth wire -neutral wire -outer insulation -cable grip -fuse -live wire -pins
58
What is the function of the earth wire and what materials are they made of
-Function: for safety, provides a low resistance connection from the outer case to the ground -material: copper coated in striped (green and yellow) plastic- ductile, flexible, good conductor -plastic insulates the wire
59
What is the function of the neutral wire and what materials are they made of
-function: completes the circuit -material: copper coated in blue/black plastic- ductile, flexible, good conductor -plastic insulates wire
60
What is the function of the live wire and what materials are they made of
-function: energy comes into the appliance, high voltage and current goes into the circuit -material: copper coated in brown/red plastic- ductile, flexible, good conductor -plastic insulates the wire
61
What is the function of the outer insulation and what materials is it made from
-function: safety, provides additional insulation to prevent shocks -material: plastic- insulating material, flexible
62
What is the function of the cable grip and what materials are they made from
-function: safety to hold the cable in place so wire does not become loose -material: plastic-insulator
63
What is the function of the fuse and what materials are they made from
-function: safety, breaks the circuit if too much current flows by melting a thin wire so the appliance no longer turns on. Has a one time use -always on same side as live wire
64
What are the three pins, functions and what materials are they made from
-earth pin, neutral pin, live pin -the earth pin is the longest to connect the earth wire first -function: inserts into the wall to make electrical connections -material: brass-conductor, durable, tough (inflexible) so they don’t bend
65
How do you decide what rating of fuse to use
-find usual operation current on the back of the plug -voltage always= 230V -power rating changes e.g 100W -calculate current using P=IV then select a fuse with a value just above e.g 1A
66
What is double insulation
-where the entire outer casing is made of plastic so it is entirely an insulator -when this is used an earth wire is not needed as the current cannot travel through the case -however if the case becomes damages it must be replaced for safety
67
What is a circuit breaker
-a safety device which turns off electricity if the current becomes too high -it is reusable but expensive -it works when: the current increases, the electromagnet strength increases so it attracts the contact opening the switch
68
Label diagram of circuit breaker
🪱
69
What is resistive heating
-when a high current is passed through a resistor it results in an electrical transfer of energy and and increase in temperature causing a heating effect -due to P=I^2R and power=energy per second -energy is transferred by heating due to collisions with vibrating ions -this can be used in electrical heaters, electrical blankets -however it is dangerous if there is too much heat: can start a fire
70
What is conventional current
The flow of charge from positive to negative
71
What is electron flow
The direction that the electrons actually move e.g negative to positive
72
What is direct current
-current that flows in one direction only -e.g battery or a cell -no variation in current/voltage supplied through the battery
73
What is alternating current
-current that changes direction in a regular pattern/interval -e.g mains electricity
74
What is the peak voltage on an oscilloscope
The amplitude of the waveform (from the middle line)
75
What are the rules of a parallel circuit
1. Total current is the sum of the current in each loop 2. Potential difference (voltage) is the same in each loop 3. Total resistance reduces as the number of loops increase (bc there are more pathways for the current to flow so it’s easier for current to flow therefore lower resistance) 4. If the thing on each loop of the circuit are the same e.g bulbs or resistors, the current slits equally
76
What are the advantages of a series circuit
-cheaper to make -less wire
77
What are the disadvantages of a series circuit
-if one bulb breaks, the whole circuit turns off -the whole circuit is either on or off
78
What are the advantages of a parallel circuit
-if one bulb breaks the rest stay on -can turn off one component if needed and not all components
79
What are the disadvantages of a parallel circuit
-expensive to make -require more wire
80
Why is current conserved at a junction
-as charge cannot be destroyed -(the charge, electrons, must have a continuous path and cannot build up of be destroyed)
81
What is the method of core prac 3: investigating how insulating materials can be charged by friction
1. Record the names of the plastics being tested in the results table 2.secure the retort stand and clamp to the lab bench with the G-clamp and hand the paper or card sling from the clamp 3. Spread out small squares of tissue paper on the laboratory bench and check that none of the rods have an initial charge by bringing them close to, but not touching, the tissue paper. If the rod attracts the small pieces of paper, then it already has some charged and should be discharged. Repeats until all plastic rods are definitely discharged 4. Charge the polythene rod using friction by rubbing it vigorously with the woollen duster forwards and backwards for at least 30 seconds 5. Without letting the rod touch any other object, place the charge polythene rod carefully into the paper sling 6. Charge one of the remaining rods by the same process in step 4 7. Without the rod touching any other object bring the newly charged rod close too, but not touching, the suspended polythene rod and observe and record results 8. Repeat the whole experiment using different types of plastic rods and record results
82
What are the disadvantages of core prac 3: investigating how insulating materials can be charged by friction
-suspended rod keeps moving due to twisting in the string -accidentally contacting other conductors so insulator can lose charge -water vapour in the air can act to dissipate charge
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