ELECTRITICITY

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Electronic components

Summary

Component in the circuit

Capacitor

Capacitor can store an electrical charge for a period of time. The larger the capacitance the more charge it can store.

Applications of capacitors  Smoothing AC voltages into steady DC voltages.  Filtering electrical noises.  Timing applications.  Short term electrical memory.

Resistor

Limit the level of currents that passes through it in order for other components to work properly

The value of the resistor is marked on it by a color code .

Resistors that work with high currents are physically bigger

Variable Resistor

Resistor with changing resistance

Diode

If connected the wrong way  no current flows.

Need more than 0.7 Volts across a diode to "turn on" allowing current to flow.

The diode has a very high resistance in one direction . The current can only flow in the other direction .

Store an electrical charge for a period of time

LDR

LDR (Light Dependent Resistor)

LDR used to detect light levels. Their resistance changes according to light. In low light , LDR has high resistance. In bright light , LDR has low resistance

LED

LED – Light Emitting Diode

Works the same as diode , has light when current passes through it. Gives off light and are often used for indicator lights in electrical equipment such as computers and electric devices. Consume very small current (energy efficient).

Transistor

Transistors have three leads: emitter, collector, base. The base controls the transistor. Transistor works as an electronic switch or an amplifier (increase current).

Ammeter

Measure current (connected in series)

Thermistor

Thermistors are used as temperature sensors , for example, in fire alarms. Their resistance changes according to temperature. At low temperatures , thermistors have high resistance. At high temperatures , thermistors have low resistance.

Integrated Circuits (IC)  microchip

These are tiny circuits attached to a piece of silicon or chip in a plastic package. The circuits inside the package contain hundreds of tiny resistor, diodes, transistors etc. They are arranged in different configurations for specific purposes.

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current,voltage,resistance

Electricity is a form of energy There are 3 main sources of electricity

Batteries

Transform Chemical energy to electrical energy

Solar cell

Transform Solar energy to electrical energy

Dynamo / Generator

Transform Kinetic energy to electrical energy

Static Electricity

Different charges - attract Same charges - repel

Electrostatics

Produced by - friction . Detected by - electroscope .

The Structure of the Atom

Current,Voltage,Resistance

Current

1) What is the definition of electric current? Electric current (I) – the rate of flow of charge (electrons). The amount of charge passing any point in a circuit in a period of time.

2) What is the unit to measure electric current? Unit: [A] Ampere

3) Who discovered current? Andre-Marie Ampere

4) Which device do we use to measure current? Current is measured by ammeter (Ampere meter)

Voltage

1) What is the definition of electric voltage? Voltage (V) – A potential difference between two points. We need energy to move the electrons between the atoms.

2) What is the unit of voltage? Unit: [V] Volt

3) Who discovered voltage? Alessandro Giuseppe Antonio Anastasio Volta

4) Which device do we use to measure voltage? Voltage is measured by voltmete

Resistance

Electrical resistance is like friction in a wire. It opposes the flow of charges in a circuit. Same as friction, it causes heating effect. The symbol of resistance is R . Unit: [Ω] - Ohm

Superconductor - allow the charges to flow easily. Resistor - resist the flow of charges. Insulator - does not allow charges to flow through it.

1) What is electrical resistance? Resistance opposes the flow of charges in a circuit.

2) What is the unit of resistance? Unit: [Ω] Ohm

4) What are the effects caused by electrical resistance? (What does resistance cause?) Resistance reduces the amount of charge that can flow in a conductor and cause heat.

3) Who discovered resistance? George Simon Ohm

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Ohm's Law

Increase of voltage increases current Increase of resistance reduces current

Resistance doesn’t affect the voltage but increase in resistance reduces the current.

Greater resistance decreases the current. Greater voltage increases the current.

Measuring Current - Ammeter Ammeter is connected in series (same line) Ammeter has very low resistance >>> Does not affect the current

Measuring Voltage - Voltmeter Voltmeter is connected in parallel (another branch) Voltmeter has Very high resistance >>> Does not affect the voltage

Resistance

Resistors in Series

Resistors in series cause more resistance to the current. Combined resistance equals the sum of all resistances. Also called:  Efficient resistance  Total resistance

RT = R1 + R2 + R3 + … Rn

Resistors in Parallel

The combined resistance is smaller than the smallest resistor.

resistors in combination (series and parallel)

Steps to follow when solving mixed circuit A real circuit is usually a mix of series and parallel in one circuit  Divide the circuits to small parts.  Start with parts that do not affect other parts.  Simply the circuits as you go.

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Circuit

Electric Symbols

Series Circuits

Ammeter is always connected in series Ammeter has very low resistance which doesn’t affect the current.

In series circuit the voltage of the batteries is the sum of all voltages VT = V1 + V2 + V3

The current is the same in every point of a series circuit. IT = I1 = I2 = I3

Parallel Circuits

The components are connected in branches. Voltmeter is always connected in parallel . Voltmeter has very high resistance which doesn’t affect the circuit because current can’t pass through it.

In parallel circuit, the voltage of the batteries is the same in every branch.

The current in the circuit is the sum of currents from all the branches. IT = I1 + I2 + I3