# Electricity

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Electricity

## 1. Electrostatic Charge Negative / Positive

### 1.1. The charges that become charged when they are rubbed. (Become an Ion)

1.1.1. Positive vs. Positive Negative vs. Negative

1.1.1.1. Perspex (+) + Perspex (+) = Repel Polythene (-) + Polythene (-) = Repel

1.1.2. Positive vs. Negative

1.1.2.1. Polythene + Woolen Cloth

1.1.2.1.1. Woolen Cloth (+) , Polythene (-) Polythene -> (+) + Woolen Cloth

1.1.2.2. Perspex + Woolen Cloth

1.1.2.2.1. Woolen Cloth (-) , Perspex (+) Perspex -> Woolen Cloth - (+)

### 1.2. Useful Websites

1.2.2. http://www.vtaide.com/png/atom.htm

### 1.3. Where does the charges come from?

1.3.1. Atom

1.3.1.1. contain of Nucleus (Proton & Neutron) and Electrons

1.3.1.1.1. Electrons : Have negative (-) charge. -- Mass 0 Protons : Have an equal positive (+) charge. -- Mass 1 Neutrons : Have no charge -- Mass 1

1.3.1.2. Equal number of Proton and Electron = Neutral = Doesn't contain any electrical charge = = Net (Overall) Charge is 0.

1.3.1.2.1. Electrons may be transferred from one to another (When Rubbed Together -- Electrostatic Charges (Static Electricity)

### 1.4. Questions?

1.4.1. What is the relationship between (-) charge and (+) charge in a neutral object?

1.4.1.1. The number of the (-) charge and (+) charge are the same. They carry no charge.

1.4.2. What happends if you bring the Perspex that is already rubbed with woolen cloth and the Polythene that is already rubbed with the woolen cloth as well?

1.4.2.1. The Perspex will be positively charged and the Polythene will be negatively charge, and since they have different charges, they will be attracted.

## 2. Conductors and insulators

### 2.1. Conductors

2.1.1. Metals -> Let elecrtons pass through -> Electrons held loosely

2.1.1.1. Good Conductors - Silver - Copper - Aluminum - Carbon

2.1.1.2. Poor Conductors - Water - Human Body - Earth - Non metal

### 2.2. Insulators

2.2.1. Plastics & Glass & Rubber & Dry Air -> Hardly conduct at all -> Electrons held tightly -> Easy to charge by rubbing

### 2.3. Semiconductors

2.3.1. Silicon & Germanium -> In-between materials -> Poor conductors when cold -> Better Conductors when warm

### 2.4. Questions

2.4.1. Why is it easy to charge perspex by rubbing, but not copper?

2.4.1.1. Perspex is an insulator that gains electrons by rubbing but copper is a conductor which lets electrons pass through them.

## 3. Induced Charges and Earthing

### 3.1. Earthed

3.1.1. Connected to the ground by a conducting material Hazards like lightings (Sparks) are earthed by Earth

3.1.1.1. Unwanted charge (-) flows away by Earthing. Flows through earth's ground

3.1.2. The charged that are induced in sphere is Earthed by finger

3.1.2.1. The electrons flow in to replace missing electrons

### 3.2. Induced Charges

3.2.1. Charges that appear on an uncharged object because of a charged object nearby

3.2.1.1. Induction

3.2.1.1.1. Sphere ends up with an opposite charge to that on the rod

3.2.1.1.2. Rod never touches the sphere

### 3.3. Useful Sites

3.3.2. http://www.s-cool.co.uk/gcse/physics/static-and-current-electricity/revise-it/static-electricity

### 3.4. Questions?

3.4.1. There is a shpere that is neutral. This means they have same number of electrons and neutrons. If you bring a rod that is negatively charged close to the sphere, then what changes take place in the sphere? Remember that the rod is not touching the sphere.

3.4.1.1. The rod is negatively charged, so it attracts the positive charge and repells the negative charge. There are same number of negative charges and the positive charges. But as the negatively charged rod gets closer, the negatively charged electrons in the sphere gets repeled, so all the negative charge gets crammed into the other end of the ephere. The positive charges cannot move, so as a result, one side of the sphere is negavely charged and the other side of the sphere is positively charged.

3.4.1.2. If we put a hand on the sphere, then the process of Earthing takes place, since the electrons flows out from the sphere to the hand to make the sphere neutral.

## 4. Electric Fields

### 4.1. The boundaries that someone or someting can feel an electric charge

4.1.1. Negative Electric fields vs. Positive Electric Fields (Field Lines)

4.1.1.1. Positive : Ourward Force Negative : Inward Force

### 4.2. Charges most concerntrated at the sharpest curve

4.2.1. Electric Field is the strongest

### 4.3. Useful Websites

4.3.1. http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/magnets_electric_effects/revision/1/

## 5. Components in a Circuit

### 5.1. Current

5.1.1. A flow of Charge Higher Current = Greater Flow of Charge

5.1.1.1. SI Unit of Current: Ampere (A)

5.1.1.1.1. Measured by connecting an Ammeter

5.1.1.2. Current is the same at all points in a simple circuit

5.1.1.3. Conventional Current Direction (= Equivalent to the direction of transfer of positive charve

5.1.1.3.1. The arrows on some circuit diagrams show the conventional Current Direction The Direction from + to - round the circuit

5.1.1.3.2. Opposite direction of the direction of the Electrons

5.1.2. Useful websites

5.1.2.1. http://en.wikibooks.org/wiki/GCSE_Science/Current,_voltage_resistance_and_Ohm's_law

5.1.2.3. http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/electricityintheory/voltagecurrentresistancerev2.shtml

### 5.2. Charge

5.2.1. (-) Electrons...?

5.2.1.1. SI Unit of Charge: Coulomb (C)

5.2.1.2. Charge = Current x Time (C) = (A) x (s)

5.2.2. Useful Websites

5.2.2.1. http://en.wikibooks.org/wiki/GCSE_Science/Current,_voltage_resistance_and_Ohm's_law

5.2.2.2. http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/electricityintheory/voltagecurrentresistancerev2.shtml

5.2.3. Questions

5.2.3.1. What charge is delivered if --> A current of 20A flows for 6 seconds

5.2.3.1.1. C=As so, 20 x 6 = 120C 120 C of charge is delivered

5.2.3.2. 60C of Charge has been delivered during 5 seconds. What is the current?

5.2.3.2.1. C= As so, 60/5 = 12 12 A is the current

### 5.3. Vlotage (Potnetial Difference)

5.3.1. Amount of Energy Higher Voltage = More energy it gives to the electrons pushed out

5.3.1.1. SI Unit of Voltage: Volt (V)

5.3.1.1.1. Measured by Voltmeter

5.3.2. Electromotive Force (EMF)

5.3.2.1. Maximum PD (Potential Difference)

5.3.2.1.1. The cell (Battery) produces the highest PD when not in a circit and not supplying the current.

5.3.3. Like every battery, every balb has its PD across it

5.3.3.1. If a balb has a PD of 1 volt across it, then 1 joule od potential energy is spent by each coloumb of charge passing thought it.

5.3.3.1.1. As the electrons flow through two bulbs, they lose some of their potnetial energy in he first bulb and the rest in the second. ( Series )

5.3.3.2. Connected in series = Produce higher PD

5.3.4. Useful Websites

5.3.4.1. http://en.wikibooks.org/wiki/GCSE_Science/Current,_voltage_resistance_and_Ohm's_law

5.3.4.3. http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/electricityintheory/voltagecurrentresistancerev2.shtml

5.3.5. Questions

5.3.5.1. If the battery reads 12V, and has two lighbulbs A and B in a series. If the lightbulb A has used up 5V and the Ammeter at the end of the circuit has its point to 3A, then what is the Voltage at the lightbulb B?

5.3.5.1.1. The total voltage is 12V. But 5V has been used by the lighbulb A.Then the Ammeter reads 3A. 12 = 5 + 3 + B 12 - 8 = B 4 = B As a result the lightbulb B has used up 4V

### 5.4. Resistance

5.4.1. SI Unit of resistance: Ohm (SIgn shaped like a lightbulb)

5.4.1.1. Resistance = PD across conductor(V) / Current through conductor(A)

5.4.1.1.1. R = V / I

5.4.1.2. Factors that Affect Resistance

5.4.1.2.1. Lengh

5.4.1.2.2. Cross-Sectional area (Thickness)

5.4.1.2.3. Material

5.4.1.2.4. Temperature

5.4.1.3. Resistance compononts

5.4.1.3.1. Resistors

5.4.1.3.2. Variable resistors (Rheostats)

5.4.1.3.3. Termistors

5.4.1.3.4. Light-dependent resistors (LDRs)

5.4.1.3.5. Diodes

5.4.1.4. Ohm's Law

5.4.1.4.1. The current is porportional to the PD (Potential Differenece)

5.4.1.4.2. Current-PD graghs

5.4.2. Useful Websites

5.4.2.2. http://en.wikibooks.org/wiki/GCSE_Science/Current,_voltage_resistance_and_Ohm's_law

5.4.2.4. http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/electricityintheory/voltagecurrentresistancerev2.shtml

## 6. Series and Parallel Circuits

### 6.1. Series Circuit

6.1.1. The bulbs share the PD(Voltage) from the battery, so each glows dimmly If one bulb is removed, the other goes out becasue the circuit is broken

6.1.1.1. WHEN RESISTORS OR OTHER COMPONENTS ARE IN SERIES -- The curren through each of the component is the same -- THe total PD (Voltage) across all the compononts is the sum of the PDs across each of them

6.1.1.1.1. Curren : Same Voltage : DIfferent

6.1.2. Calculating Resistance

6.1.2.1. R = R1 + R2 + R3

### 6.2. Parallel Circuit

6.2.1. Each gets gullPD from the battery because each is connected diretly to it If one bulb is removed, the other keeps working because it is still part of an unbroken circuit

6.2.1.1. WHEN RESISTORS OR OTHER COMPONENTS ARE IN PARALLEL -- The PD (Voltage) across each of the component is the same -- THe total current in the main circuit is the sum of the currents in the branches

6.2.1.1.1. Current : DIfferent Voltage : Same

6.2.2. Calculating Resistance

6.2.2.1. R= 1/R1 + 1/R2 + 1/R3 R = R1 x R2 ㅡㅡㅡㅡ R1 + R2

### 6.4. Questions

6.4.1. What is the total resistance in a series circuit if the R1 is 3Ohm R2 is 4Ohm and R3 is 6Ohm?

6.4.1.1. 3 + 4 + 6 = 13 Ohm

6.4.2. What is the total resistance in a parallel circuir if the R1 is 3Ohm R2 is 4Ohm an R3 is 6Ohm?

6.4.2.1. 4/3 Ohm

## 7. Electrical Power

### 7.1. Power

7.1.1. Power : The rate at which the energy is transformed SI Unit of Power : Watt (W) Power = Energy Transformed / Time taken = Current2 x resistance

### 7.2. Alternating Current (Mains Electricity)

7.2.1. The mains current tha flows backwards and forwards constantly (50 times per second) The main frequency is 50 Hz)

7.2.2. Switch

7.2.2.1. Works equally well when neutral

7.2.3. Fuse

7.2.3.1. Thin peice of wire which overhears and melts if the current is too high If the current gets too high, the fuse breaks the circuit before the cable can overheat cand catch fire

7.2.3.2. But many circuits use a circuit breaker instead of fuse

7.2.4. Double Insulation

7.2.4.1. Some appliances (Radios etc.) Do not have an earth wire. Their outer case is covered with plastic rather than metal. --> THe plastic acts as an extra layer of insulation around the wires

### 7.4. Questions

7.4.1. There is a series circuit and it has two lightbulbs A with 4V and B with 6V. If the Ammeter shows 2A, then what is the power in each of the lighbullbs?

7.4.1.1. P = VA SO, Bulb A --> 4 x 2 = 8W Bulb B --> 6 x 2 = 12W