revision: Physics - Topic 2

Formulae-
P = V × I
power = voltage × current
(REMEMBER -> Phantom Virus)

E = V × I × t
energy transferred = voltage × current × time
or
E = P × t
energy transferred = power (voltage × current) × time

V = I × R
voltage = current × resistance
(REMEMBER -> VIRus)

Q = I × t
charge = current x time
(REMEMBER -> Don't QUIT!)

(Phantom Virus...evit no...emit...viruses and...never quit. Mwaha)

V = E/Q
voltage = energy transferred/charge

2a) Units
2.1 - use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), seconds (s), volt (V), watt (W)

Ampere (A) - current (I)
Coulomb (C) - charge (Q)
Joule (J) - energy (E)
Ohm (Ω) - resistance (R)
Seconds (s) - time (t)
Volt (V) - voltage (V)
Watt (W) - power (P)

2b) Mains Electricity
2.2 - understand and identify the hazards of electricity including frayed cables, long cables, damaged plugs, water around sockets, and pushing metal objects into sockets (why would anyone do that? -_-"")

frayed cables - if the insulation around the wire is damaged, you could expose the metal wires and come into contact with them. With the current passing through, you would get an electric shock.

long cables - you could possible trip? I'm not sure. But if it's the kite thingy near high voltage power lines then it's the case where the current could travel down the string and if you are in contact with the string, you would also get electric shock.

damaged plugs - If the plug is damaged, there is a possibility of you touching the components that are exposed in the plug, again with current passing through, you will get an electric shock.

water around sockets - water is a conductor of electricity, with water around sockets coming in contact with electrical appliances or the socket, the current could pass through and you will get an electric shock.

pushing metal objects into sockets - (IDIOT. Who would do this? -.-") Again, metals are conductors and therefore current can pass through and if you were in contact...you'd get electrocuted.

=Basically, the dangers are electric shock. (I'm in shock, e-e-lectric shock, nananananana....f(x) anyone? :D)

2.3 - understand the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances.

insulation - usually made of plastic, there as protection to prevent the wires and things from being exposed.

double insulation - wires of the appliance is insulated and so is the casing of the appliance, examples are computer monitors and such. It is when an appliance has a casing that is an insulator.This provides even more protection.

earthing - if the current is too large it flows down the earth wire, connected to the metal casing of the appliance, this blows the fuses, breaking the circuit and prevents fires.

fuses - made of a thin piece of wire, if the current is too high the fuse gets hot and melts. When the fuse blows, the circuit is broken.

circuit breakers - used rather than fuses as they perform the same job...when a specific current size is exceeded it breaks the circuit. The big bro of a fuse.

2.4 - understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts.

It's straightforward...but
If the resistor increases, the current decreases...and vice versa.
Anyways, when current passes through a wire the electrical energy is converted into heat/thermal energy. For example - kettles, irons, hairdryers, etc. The wires of these appliances have very low resistance so no energy is wasted in conversion. They still have resistance, however, and if the current is too large, they will get hot and can cause fires.

2.5 - know and use the relationship: P = V × I (power = voltage × current) and apply the relationship to the selection of appropriate fuses.

Remember that POWER is measured in watts, CURRENT in amps and VOLTAGE in voltages. Units give you marks!!

POWER - is the rate of energy transferred or converted every second.
CURRENT - is the rate of flow of electrons
VOLTAGE - is the the energy transferred from one coulomb of charge. 1 volt is 1 joule per coulomb.


1000W = 1kW
1,000,000W = 1MW

Basically, if the average current is like 10A, then you would use like a 13A fuse. Gotta be more or your circuit ain't gonna work at all. DUH!


2.6 - use the relationship between energy transferred, current, voltage and time: E = V × I × t (energy transferred = voltage × current × time) or E = P × t (energy transferred = power (voltage × current) × time)

ENERGY is measured in joules, CURRENT in amps, VOLTAGE in volts, POWER in watts and TIME in seconds. Remember to convert minutes to seconds by multiplying 60.


2.7 - understand the difference between main electricity being alternating current (a.c) and direct current (d.c.) being supplied by a cell or battery.

A battery supplying direct current allows current to flow in only one directions.
HAHA How about this? To listen to 1D you gotta have battery left on your iPod, iPhone, whatever.

Mains electricity which supplies alternating current, which changes direction constantly.

2c) Energy and potential difference in circuits
2.8 - explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting.

In a series circuit, current flows through 1 route. If there is a fault in the circuit at any point, be it switches turned off or lamps which are blown, the current cannot flow through and all the components in the circuit will not work.

In a parallel circuit, there are intersections where current can split to multiple routes. If a lamp blows, nothing else will go out as the current has other routes.

This is useful for lighting units in houses and such as if one bulb goes out, not all of them will.

2.9 - understand that the current in a series circuit depends on the applied voltage and the number and nature of other components.


Identical components get an equal share of the voltage and will have the same brightness.

If you can't remember -> use ASS. MWAHAAHA A = current is the SAME in SERIES. If current is the same then voltage is shared :D :D :D And I don't understand why festive bulbs are series but that's the example haha.



And parallel, this is the opposite. Just remember ASS and parallel is the opposite. So...Current is shared and Voltage is equal.

2.10 - describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally.

Ohm's law is when current is directly proportional to the voltage at constant temperature.
The graphs will always look like this: (a straight line that passes through the origin (0,0). Larger gradient means less resistance.

Wires and resistors obey Ohm's law and the current will be directly proportional to the voltage so we call them Ohmic components.

In a filament lamp, the resistance of a metal increases with it's temperature...the filament wire gets hot as there are more collisions between the metal ions and electrons it's resistance also increases. The current decreases as the resistance does so the gradient is less steep.


Diodes allow electricity to flow in only one direction and have large resistances if it is the wrong direction. Therefore, there is a horizontal line where the voltage is negative.
(I think 1D fan club should be called 'diodes' haha)
As the resistance is small in the right direction, the graph becomes very steep.

2.11 - describe the qualitative effect of changing resistance on the current in a circuit.

Just remember.
Increase resistance = decrease current
And vice versa. Qualitative means to describe that in words.
When the resistance increases the current decreases.

END.

2.12 - describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature.

Again. Remember.
LDRs - LIGHT DEPENDENT RESISTORS!!!!!!!!!!
LIGHT - LOW resistance
DARK - HIGH resistance

Thermistors -
COLD - HIGH resistance
HOT - LOW resistance

DARK AND COLD = HIGH. Dark places are cold.

Again, qualitative means to describe with words.

END.

2.13 - know that lamps and LEDs can be used to indicate the presence of a current in a circuit.

LED are diodes, light emitting ones. So...can indicate the presence of current if placed in the right directions because they're light up (my world like nobody else. OMG -.- Why is there so much 1D in this topic...)
Lamps work too...they just light up. HAHAHA


2.14 - know and use the relationship between voltage current and resistance: 


V = I × R
voltage (volts) = current (amps) × resistance (ohms)
(REMEMBER -> VIRus)

2.15 - understand that current is the rate of flow of charge.

That's basically what current is. REMEMBER IT.

2.16 - know and use the relationship between charge, current and time:



Q = I × t
charge (C) = current (A) x time (s)
(REMEMBER -> Don't QUIT!)

2.17 - know that electric current in solid metal conductors is a flow of negatively charged electrons.

Conventional current - positive particles are repelled by the positive terminal and attract the negative.
State that it is conventional and they are 'imaginary' positive charges that flow from + to -

Actual current - the flow of electrons which are negatively charged and therefore are attracted to the positive terminal.

2.18 - understand that: 
-voltage is the energy transferred per unit charge passed
-the volt is a joule per coulomb.



V = E/Q
voltage = energy transferred/charge
1V = 1J/C

2d) Electric Charge
2.19 - identify common materials which are electrical conductors or insulators, including metals and plastics

Insulators	Conductors
Air	Metal
Plastic (used to encase electric wires)	Copper (used in wires)
Rubber (used to encase older plugs)	Brass (used in pins on plugs)
paper	Water (don't use your hair drier in the bath!)
Dry wood	Wet wood

2.20 - describe experiments to investigate how insulating materials can be charged by friction.
2.21 - explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons
BENDING WATER!!! MAGIC HAHA THAT EXPLAINS IT!

If you rub a balloon on a jumper the balloon will stick to the wall.because it becomes charged.

Rubbing an insulating material on cloth with charge the insulating materials as electrons are transferred. They then become charged either negatively or positively depending on whether they gain or loss electrons. If it loses electrons it becomes positively charged. If it gains electrons it become negatively charged.

2.22 - understand that there are forces of attraction between unlike charges and forces of repulsion between like charges.

like charges repel, unlike charges attract.
OPPOSITES ATTRACT :D

2.23 - explain electrostatic phenomena in terms of the movement of electrons.
-When an object gains electrons and becomes negatively charge, it will repel other negatively charges objects and attract positively charged ones.

A charged object will always attract uncharged objects.
If you rub a balloon on a jumper the balloon will stick to the wall.because it becomes charged but the wall is still uncharged. This is because there are positively charged protons in the uncharged object that attract the negatively charged object.

2.24 - explain the potential dangers of electrostatic charges, eg. when fuelling aircraft and tankers.

Static charge can build up while fuelling, and if a spark occurs BOOOOOOOOOOOMM!!! or FIRE!!
To prevent this, the tanker or plane are earthed to prevent this from happening.

2.25 - explain some of the uses of electrostatic charges, eg. in photocopiers and inkjet printers.

inkjet printers - ink drops that are charged can be directed to specific places on the paper by using charged plates.

photocopiers - ... It's long...Umm...The drum is charges positively and an image is projected on it so only the dark parts stay charged, negatively charged powder ink sticks to the charged parts...that ink is then transferred to another piece of paper and heat rollers are used for the ink to stick.

paint spraying - paint droplets are given charge and the object to be painted is given the opposite charge.