Physics 2b flashcards

?
  • Created by: Evie
  • Created on: 28-04-13 12:49
How does something become static?
When insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other. This leaves a - static charge on one and a + static charge on the other.
1 of 67
What is current? Unit?
The flow of electric charge round a circuit. It will only flow through a component if theres a voltage. Amphere(A)
2 of 67
What is the voltage/potential difference? Unit?
The driving force that pushes the current round. Volts(V)
3 of 67
What is resistance? Unit?
Anything that slows down the flow. The greater it is across a component, the smaller the current that flows. Unit is ohm(Ω)
4 of 67
Whats the equation for current?
Charge(C) // Time(s) or I=Q/t
5 of 67
Whats the equation for voltage?
work done // charge. or v=W/Q
6 of 67
What do different resistors look like on a current/voltage graph(I/V)? Why?
Straight diagonal lines. The current through a resistor is directly proportional to voltage. Different resistors=different resistances, hence different slopes. The steeper the graph, the lower the resistance.
7 of 67
What does a filament lamp look like on an I/V graph? Why?
As the temperature of the filament increases, the resistance increases, hence the curve.
8 of 67
What does a diode look like on a I/V graph? Why?
A steep curve in the positive quarter. Current will only flow through a diode in one direction. It has a very high resistance in the opposite direction.
9 of 67
Explain how resistance increases with temperature.
Charge flows through a resistor, some of the energy transfers to heat which causes the ions to vibrate more. This makes it harder for the electrons to get through the resistor, so the current can't flow easily and the resistance increases.
10 of 67
Explain how resistance increases with temperature. (summary)
More current means an increase in temperature, which means an increase in resistance, which means the current decreases again.
11 of 67
What is the equation for voltage (in circuits)
Current(A) x resistance(ohms)
12 of 67
What is a diode?
A device made from a semiconductor material used to regulate voltage in circuits. It lets the current flow freely through it in ONE direction.
13 of 67
What is an LED? What are they used for?
Diodes which emit light when a current flows through it in a forward direction. Used for lighting as they use a smaller current. They indicate the presence of current in a circuit. Used in traffic lights, remotes & numbers in digital alarm clocks.
14 of 67
What is an LDR? What are they used for?
Light-dedpendant resistors are dependent on light intensity. In bright light, the resistance falls. In darkness, resistance is highest. Used in automatic night lights, outdoor lights & burglar detectors.
15 of 67
What are thermistors? What are they used for?
They are dependant on temperature. In heat, the resistance drops. In the cool, the resistance rises. They make useful temperature detectors like car engine temp censors or electronic thermostats.
16 of 67
5 facts about series circuits.
If you remove one part, its broken. The different parts are connected by a line between +ve and -ve power. Total PD is shared/added up. Current is the same everywhere. Resistance has to be added up.
17 of 67
5 facts about parallel circuits.
Components are separately connected to the +ve and -ve power. Voltage is the same everywhere. Current is shared/has to be added up. Everything can be turned on/off separately. Everything gets full voltage from battery.
18 of 67
What is AC/DC? How many volts is the mains supply and what frequency does it have??
Alternating current (main supply) - constantly changing direction. and direct current (battery supply)- flows in 1 direction. Frequency=50Hz. 230V.
19 of 67
What does the DC look like on a cathode ray oscilloscope?
Always at a straight line because its always the same voltage.
20 of 67
What does the AC look like on a CRO?
Regular pattern. The trace goes up and down, positive, negative. The vertical height shows the input voltage at that point.
21 of 67
What are the features of a CRO? What is the time period?
Gain dial controls how many volts each cm division represents on the y-axis. The timebase dial controls how many milliseconds each division represents on the x-axis(1ms=0.0001s). The time period is the time taken to complete one cycle.
22 of 67
How do you find the frequency of a CRO trace?
1 // time period (s)
23 of 67
Name 8 hazards in the home.
Long cables, cables in contact with heat/water, shoving into sockets, plug overload, non-covered appliances, frayed cables, damaged plugs & lighting sockets without bulbs in.
24 of 67
What are the features of 3-core cables?
Brown live wire in a mains supply alternates between -ve and +ve voltage. Blue neutral wire=0V. Electricity normally flows in/out through live/neutral wires only. Earth wire for safety.
25 of 67
How is a plug wired safely? What are some features of plugs?
Right coloured wire connected to each pin, firmly screwed in. No bare wires. Cable grip fastened tightly. Thicker cables have less resistance thus more current. Metal parts made from copper/brass/good conductors. Covering made from rubber or plastic
26 of 67
How does earthing work?
A fault allows the live wire to touch the metal case. Big current now flows out through earth wire, causing a big current surge. Big surge blows fuse and isolates appliance from the live, stopping any electric shocks.
27 of 67
What are 2-core cables?
Cables that are double-insulated. They only carry a live and neutral wire.
28 of 67
How do circuit breakers work? Give an example of one and what are the advantages/disadvantages of it?
They break the circuit by opening a switch. Replaceable but expensive. Resident Current Circuit Breakers (RCCBs) can detect smaller surges. They're immediate, you don't have to wait for anything to melt.
29 of 67
How do you calculate the energy transferred in a appliance?
power rating x time
30 of 67
How do you calculate the electrical power of something?
current x voltage
31 of 67
How do you calculate the energy transformed in something?
charge x voltage
32 of 67
What did JJ Thomson discover? What did he believe?
In the 1900s, he discovered that electrons could be removed from atoms/atoms could be broken up. He suggested that atoms where spheres of positive charge with tiny electrons stuck in them like a PLUM PUDDING.
33 of 67
What was the Rutherford-Marsden experiment? What did they expect?
They tried firing beam of alpha particles through thin gold foil. They expected most to be slightly deflected by electrons. But most went straight through and a few came bounced back to them.
34 of 67
What did they learn from the Rutherford experiment?
Most of the mass of the atom was concentrated at the centre in a tiny nucleus. The nucleus must have a positive charge since it repelled some of the alphas. Most of the atom is empty space!
35 of 67
What is radioactive decay and what is it affected by?
Radioactive substances give out radiation from the nuclei of their atoms. Its completely random. You don't know when it will start and you can't stop it. Its not affected by anything. It spits out gamma, beta, and/or alpha.
36 of 67
Where does background radiation come from naturally/man made? Percentages?
Unstable isotopes in food(12%), air, rocks & building materials(14%), radon gas(51%) and cosmic rays (10%). Only 1% comes from the nuclear industry (waste, accidents, weapon tests).
37 of 67
What are alpha particles and what properties do they have?
2 neutrons and 2 protons (helium nuclei). Big, heavy, slow moving so they don't penetrate far into materials or air. Because of the size, they're strongly ionising.
38 of 67
What does strongly ionising mean?
They bash into a lot of atoms and knock electrons off them before they slow down, creating lots of ions.
39 of 67
What are beta particles and what properties do they have?
Electrons! Quite fast and small. Penetrate moderately into materials before colliding. Long range in air. Moderately ionising. Almost no mass. - charge. For every b-particle emitted, a neutron turns into a proton (in the nucleus of new atom).
40 of 67
What are gamma rays and what properties do they have?
Short wavelength electromagnetic waves. They penetrate far into materials without being stopped and pass straight through air. Thus, they're weakly ionising because they tend to pass through atoms, not collide with them. No mass, no charge.
41 of 67
Give an example of alpha decay. Write the equation.
Alpha decay:
42 of 67
Give an example of beta decay. Write the equation.
Beta decay:
43 of 67
Why are alpha/beta deflected by electric and magnetic fields?
They deflect in opposite directions because they have opposite charges. α-particles have a larger charge than β-particles, and a greater force in these fields BUT they're deflected less because they have a bigger mass.
44 of 67
Give some examples of locations/occupations where you have a higher radiation dose risk
Underground rocks can release radon gas which can get trapped in houses, nuclear industry workers, radiographers in hospitals, at high altitudes cosmic rays increase (pilots), underground mines.
45 of 67
What is the radioactivity unit? What does it mean?
Becquerel(Bq). 1Bq means one nucleus decaying per second.
46 of 67
What is a half-life?
The average time it takes for the number of nuclei to halve in a radioactive isotope sample.
47 of 67
How do you use radiation in smoke detectors?
A weak source of α-radiation is placed near 2 electrodes. The source causes ionisation and a current flows through the electrodes. If there is fire then smoke will absorb the radiation - so the current stops and the alarm sounds
48 of 67
How do you use radiation for tracers in medicine?
Inject into people and their progress is followed by a detector. Iodine-131 is absorbed by the thyroid gland like normal iodine-127. It gives out radiation which shows wether the gland is absorbing iodine as it should.
49 of 67
What kind of isotopes should be taken into the body? Why?
Gamma/beta emitters. So the radiation passes out of the body, which alpha can't do. They should have a short half life so they don't stay in your body for long.
50 of 67
How do you use radiation in radiotherapy?
Since high doses of γ-raditation will kill all living cells, they can be used to treat cancers. The rays have to be directed carefully at the right dosage to kill the cancer cells only.
51 of 67
How do you use radiation in food/surgery sterilisation? What kind of isotope do you need?
Gamma will kill all microbes, keeping food for longer, not radioactive after. Medical tools can be sterilised instead of boiling. Doesn't need high temp, doesn't melt. Strong γ with long half-life so it doesn't need replacing often.
52 of 67
What isotopes are most dangerous outside the body?
Beta/Gamma. They can get inside the organs whereas alpha can't even get through the skin.
53 of 67
5 tips when handling a radioactive substance?
Use for a short time, use tongs never skin, hold at arms length, point away, store in lead box.
54 of 67
Explain nuclear fission. Which fuel/s are used?
In a reactor, a controlled chain reaction takes place where atomic nuclei are split and release energy in the form of heat. This heats water which turns to steam, driving turbines and then a electricity generator. Unranium235 or plutonium239.
55 of 67
Explain the chain reaction in nuclear fission.
A slow moving neutron must be absorbed into a uranium nucleus. This makes it unstable so it splits. In every split 2/3 neutrons are spat out. One might hit another nucleus and so it goes on.
56 of 67
How does fission produce radioactivity?
When a large atom splits in two it forms two new smaller nuclei which are usually radioactive because they have the 'wrong' number of neutrons.
57 of 67
Explain nuclear fusion.
Two light nuclei (like hydrogen) can join together to create a larger nucleus.
58 of 67
What are the pros and cons of fission?
Nuclear fuel is cheap, releases lots of energy. BUT- the products are highly radioactive+hard to store. Expensive to build power plant/final decommissioning. Dismantling a plant can take decades.
59 of 67
What are the pros and cons of fusion?
Releases more energy than fission for a given mass, doesn't leave lots of radioactive waste, lots of hydrogen available. BUT- It can only happen at really high temperatures (10,000,000C). For this and pressure you need a really strong magnetic field.
60 of 67
What happens to a red giant? What could happen to a super red giant?
It becomes a white dwarf. It becomes a supernova then it becomes a neutron star or a black hole.
61 of 67
How do stars form? What is a protostar?
Stars initially form from clouds of dust and gas. The force of gravity makes the gas and dust spiral together to make a protostar.
62 of 67
How is a main sequence star formed?
Ep is converted to heat. When it hot enough, hydrogen nuclei undergo fusion to form helium nuclei and give out of heat/light. Star enters a stable period as it consumes huge amounts of hydrogen. The heat gives pressure to balance gravity.
63 of 67
What happens after the star comes out of its stable sequence?
Eventually hydrogen will run out. Heavier elements like iron are made by the fusion of helium. It becomes red because the surface cools.
64 of 67
What happens in a supernova?
Red SUPER giants glow bright again (fusion) so they expand and contract forming elements heavier than iron and ejecting them into the universe forming new planets/stars.
65 of 67
What is a white dwarf and how does it form?
A red giant becomes unstable and ejects its outer later of dust and gas as a planetary nebula. This leaves behind a hot, dense, solid core which cools to a black dwarf and disappears.
66 of 67
What happens after a supernova?
The explosion throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If its big enough it will become a black hole.
67 of 67

Other cards in this set

Card 2

Front

What is current? Unit?

Back

The flow of electric charge round a circuit. It will only flow through a component if theres a voltage. Amphere(A)

Card 3

Front

What is the voltage/potential difference? Unit?

Back

Preview of the front of card 3

Card 4

Front

What is resistance? Unit?

Back

Preview of the front of card 4

Card 5

Front

Whats the equation for current?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Physics resources:

See all Physics resources »