➢ Energy change in electrical devices
➢ Heating effect of electric current.
➢ Joule’s Law & Mathematical problems related to these.
➢ Arrangement of Resistors in Circuits-Series Connection and Parallel Connection – Mathematical problems related to these.
➢ Electric heating appliances.
➢ Peculiarities of substances used as heating coil.
➢ Short circuit, Overloading.
➢ Working of Safety fuse.
➢ Peculiarities of substances used as fuse wire.
➢ Electric power & Mathematical problems related to these.
Heating effect of electric current:When electricity passes through any conductor, it generates heat energy.
One volt:The potential difference between two points will be one volt if one joule of work is done in moving one coulomb of charge from one point to the other.
Joule Heating or Ohmic Heating.
Heat is developed in a circuit on passing current
through it is known as the Joule Heating or Ohmic Heating.
What are the factors influencing the heat developed when a current passes through a conductor?
1. Intensity of electric current (I)
2. Resistance of the conductor (R)
3. The time of flow of current (t)
Series Connection
Effective resistance, R = R1 + R2
When resistors are connected in series,
* The potential difference gets divided
* The current through each resistor will be the same.
* The effective resistance increases.
Parallel Connection
Effective resistance, 1/R = 1/R1 + 1/R2
When resistors are connected in Parallel,
* The potential difference in each resistors are same.
* Current through each resistors are different.
* The effective resistance decreases.
5.Electric heating appliances
* Name the part in which electrical energy changes into heat energy.
– Heating coils
* Which material is used to make this part?
– Nichrome(Nichrome is an alloy of nickel, chromium and iron)
6. Peculiarities of substances used as heating coil.
* What are the peculiarities of heating coil?
– High resistivity
– Ability to remain in red hot condition for a long time without
getting oxidised
– High melting point
7. Short circuit, Overloading.
Short Circuit
If the positive and the negative terminals of a battery or the two wires from the mains come into contact without the presence of a resistance in between, they are said to be short-circuited.
Overloading
A circuit is said to be overloaded if the total power of all the
appliances connected to it is more than what the circuit can withstand.
Working of Safety fuse
Safety fuse is a device that works on the heating effect of electric current.
* Which material is used to make fuse wire?
– Fuse wire, an alloy of tin and lead,
* Which are the circumstances that cause high electric current, leading to the melting of fuse wire?
-Short Circuit and Overloading
* How is the fuse wire connected to a circuit?
– In series.
* How dose a fuse wire working?
When there is an overloading or short-circuit in the circuit.—}When electric current is increased.—} —-} According to Joule’s Law, more heat will be produced—} The fuse wire melts—} The circuit is broken
Peculiarities of substances used as fuse wire.
* What are the peculiarities of fuse wire?
-low melting point, More ductility.
* When a fuse wire is included in a household wiring, what are the precautions to be taken?
• The ends of the fuse wire must be connected firmly at
appropriate points.
• The fuse wire should not project out of the carrier base.
Electric power & Mathematical problems related to these
* The amount of energy consumed by an electrical appliance in unit time is its power.
* The unit of power is watt (W)
