# GCSE P2 Chapter 4

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- Created by: emma998
- Created on: 09-03-14 14:00

## Electrical charges

**Charging by friction**= When two**electrically insultaing materials**are rubbed together, electrons are rubbed off one of the materials and deposited on the other. The material which loses electrons becomes**positively charged**and the other gains electrons and becomes**negatively charged.**

- Materials that have
**opposite charges attract** - Materials that have
**like charges repel** - The larger the distance between the two charged objects the
**weaker**the force of attraction

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## Electric circuits

- Every component in an electric circuit has its own symbol

**Switch**= Can be opened or closed to enable the current to be switched on or off**Cell**= Necessary to**push electrons**round the circiut, a battery is made up of 2+ cells

**Ammeter**= Measures the**current**through a component, is always placed in**series****Voltmeter**= Measures**potential difference**across component, placed in**parallel**

**Diode**= Allows current through in**1 direction only**, high resitstance in the other direction**Indicator**=**Emits light**when**current**passes through as signal or used as a light source**Light emitting diode**=**Emits light**as a current passes through it

**Heater**= Transfers**electrical enrrgy**into**heat energy**as current passes through it**Fixed Resistor**=**Limits**the current to a certain value

**Variable resistor**= Allows the current to be**varied****Fuse**=**Melts and breaks**the circuit if the current exceeds a specific value

**Current(Amps(A)) = charge(Coulombs(C)) / time(Seconds(S))****I = Q / T**

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## Resistance and potential difference

**Voltmeters**measure the**potential difference**across a component and are always placed in**parallel**with the component

**Potential difference(V) = work done(J) / charge(C)****Potential difference(V) = energy transfered(J) / charge(C)****Potential difference(V) = resistance(O) X current(A)**

**Resistance**is measured in**ohms**and is a measure of how difficult it is for the electrons to pass through a component.**It is the opposition to current flow****Resistance(O) = Potential difference(V) / Current(A)**

**Current-potential difference graphs**show the relaionship between the current and potential difference**through a compnent**

- Ohm's law states that the
**current through resistor**at a**constant temperature**is**diectly proportional**to the**potential difference across it.** - Components which obey this law are said to be
**Ohmic Conductors**

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## Current-potential difference graphs

**Filament bulb** - current is not directly proportional to potential differnce across it. Because:

- As the
**current**through it**increases** - The
**temperature**increases - So
**resistance increases** - So
**potential difference**increases at a**greater rate**than the**current ( V = I X R )**

**Diode** - Current through it is not proportional to potential difference bcause:

- The
**current**through a diode can flow in**one direction only** - At a
**negative potential difference current is always zero**because**resistance in opposite direction**is extremley high - As soon as
**potential difference is positive current increases**much more than potential difference

**Light dependant resistor** - As light falling on it increases, the **resistance decreases** so in parallel circuits, **current increases at faster rate** than potential difference across it

**Thermistor** - As **temperature increases** the **resistance** of component **decreases**

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## Series circuits

- In a
**series cricuits**all components are connected**one after the other** - If there is a break anywhere in the circuit,
**charge stops flowing**

- In a series circuit
**current is the same**through each component (only one path for charge to flow)**(Current**depends on**pd of power supply**and**total resistance**of circuit -**I = V/R****)** - The larger the resistance the smaller the current

**Resistance**of the circuit is found by**adding up**the resistance of each component

**Potential difference**of each compnent is shared by each component (the components with larger resistances get a larger potential difference)- (V = I X R) -
**Larger resistance**, larger potential difference

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## Parallel circuits

- In
**parallel circuits**each component is connected**across from the supply** - There are
**several different routes**which the**charge can flow in** - If there is a break in one area of the circuit then charge will
**continue to flow**just to other areas of the circuit

The **current** through **each component varies:**

- Charge has a choice of routes
- The routes with a
**high resistance**will have a**low current**through the components - Components which have a
**low resistance**will have a much**higher curent**flowing through them**(I = V/R)**- The smaller the resistance the larger the current - The
**total current**of circuit can be found by adding up current through each component

The **potential differnce** across each component is the **same**:

- All components placed in
**parallel to the power supply** - So potential difference is the
**same**across each component

**Total resistance** of the circuit is found by **adding** up the resistance of **each component**

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