Lead acid accumulator• Car battery• Converts chemical energy to electrical energy• Rechargeable
Generation of Electricity• Bicycle Dynamo• Kinetic energy to electrical energy
Solar cell• Convert light energy to electrical energy
Electric Current• Caused by the flow of negative charges along a conductor
Why negative charges move?• Due to potential difference between 2 points of a conductor• Potential difference = Voltage Electrons move from region of Higher electron concentration to region of Lower electron concentration.
How to measure electric current?• Ammeter• Milliammeter• Connect in series (one by one)• Positive terminal ammeter – positive terminal battery• Negative terminal ammeter – negative terminal battery
Ammeter• Measures electric current• SI unit for current = Ampere (A)How to measure?? One after another – Series circuit
• The brighter the light bulb, the higher the reading of ammeter.
What are the differences between these circuits?
What is voltage?• Voltage is provided by the electrical sources• Eg. Battery, lead acid accumulator
Voltage• Measure potential difference (Voltage) between 2 points• SI unit – Volt (V)• How to connect?To measure voltage of a light bulb,we have to connect the voltmeter acrossthe light bulb – Parallel circuit
• The brighter the light bulb, the higher the reading of voltmeter.
Resistor• To restrict current flow• Used in - Radio, Television, Oven, Fan
All materials haveelectrical resistanceResistance =Frictional forceOpposes the direction of current flowGood electrical conductor = Low resistancePoor electrical conductor = High resistance
Factors affecting resistance• The length of the wire – The longer the wire, the greater the resistance• The thickness of the wire – The thicker the wire, the lesser the resistance• The type of material used – Different types of materials have different resistances • Copper and Silver • Iron and Magnesium
Factors affecting resistance• The length of the wire – The longer the wire, the greater the resistance
Factors affecting resistance• The thickness of the wire – The thicker the wire, the lesser the resistance
• The thickness of the wire – The thicker the wire, the lesser the resistance
Factors affecting resistance• The type of material used – Different types of materials have different resistances
Relationship between current and resistance• High resistance >>>> _____ current• Low resistance >>>> _____ current Length of nichrome wire Ammeter reading 20 0.9 30 0.7 40 0.5 50 0.3 60 0.1
Relationship between voltage and current• Imagine voltage as battery• Higher voltage >>> Greater current• Lower voltage >>> Lesser current
ResistanceOhm’s law – Current (I) that flows through a metal conductor is directly proportional to the potential difference (voltage) across it, if resistance remains constant
Relationship betweenCurrent, Voltage and Resistance
Series and Parallel circuit• Series – One way traffic• Parallel – More than one way
• When more light bulbs are added, the brightness of light bulb decreases.
Advantages & Disadvantages of Series Circuit – One switch can switch off everything
Parallel circuit• Each bulb receive full voltage from battery and have same brightness
Advantages and disadvantages of Parallel circuit• Other electrical appliances can still function if one of them break down