Maharashtra Board Class 10 Science Part 1 Chapter 4 Effects of electric current PDF Download

Effects Of Electric Current

We have learnt in earlier standards about static electricity. We performed various experiments regarding negatively and positively charged objects. The reason behind the object becoming positively and negatively charged is the transfer of negatively charged particles from one object to another object. In previous standard, we also studied about electric current.

In this chapter, we will study about an electric current flowing through a conducting wire, an electric current flowing through a resistor, electromagnetic induction, electric motor and generator.

Effects Of Electric Current

Energy transfer in electric circuit.

Heating effects of electric current.

Magnetic effects of electric current.

Observe And Discuss

What do you observe in the following pictures?

Which effects of electric current do you find?

Can You Recall?

How do we decide that a given material is a good conductor of electricity or is an insulator?

Iron is a conductor of electricity, but when we pick up a piece of iron resting on the ground, why don't we get electric shock?

Energy Transfer In An Electric Circuit

Materials: connecting wires, electric cells, electrical resistance, voltmeter, ammeter, plug key.

Procedure: Connect the circuit as shown in the accompanying figure 4.2 after taking the components with proper values. Measure the current (I). Also measure the potential difference (V_AB) between the two ends (A and B) of the resistance.

The potential at A is higher than the potential at B as the point A is connected to the positive electrode of the cell and the point B to the negative electrode of the cell.

If a charge Q flows from A to B, work V_AB Q, has been done on Q while going from A to B (Refer to chapter 3 of std 9). From where does the energy come to do this work? The source of energy is the cell. The cell gives this energy through the charge Q to the resistance where work V_AB Q is performed. If the charge Q flows from A to B in time t, i.e. the work is performed in time t, then during that time the energy V_AB Q is given to the resistor.

What happens to this energy? This energy is received by the resistor and is converted into heat energy, the temperature of the resistor is increased.

If in the circuit, the resistor is replaced by a motor, in which form will the energy given by the cell get transformed into?

The source of energy, the cell, gives in time t, the energy P x t to the resistor. If I is the current flowing continuously through the circuit, the heat produced in the resistor in time t will be

H = P x t = V_AB x I x t ................................ (2)

According to Ohm's law,

V_AB = I x R ................................................ (3)

H = V²_AB × \(\frac{t}{R}\) .......................................... (4)

Similarly, H = I x I x R x t = I² x Rt ......... (5)

H = I² x R x t is called Joules law of heating

Unit Of Electrical Power

P = V_AB x I = Volt x Amp ........................... (6)

1 Volt x 1 Amp = \(\frac{1J}{1C}\) x \(\frac{1C}{1s}\) ............. (7)

\(\frac{1J}{s}\) = W (watt) ...................................... (8)

Thus the unit of electrical power is 1W (watt).

Heating Effect Of Electric Current

When a resistor is connected in an electrical circuit, heat is produced in it due to the current. This is known as the heating effect of current.

Teacher's Note

Electric heaters and bulbs use heat from electric current. Your home heater uses the same idea to keep water warm.

Exam Trick

Remember: H = I²Rt means more current creates more heat. Like a crowded bus gets hot!

Points To Remember

Heat is produced when electric current flows through a resistor.
Higher current produces more heat energy.
Joule's law helps us calculate the heat produced.
Electric bulbs, heaters, and cookers use this heating effect.
The unit of power is Watt (W).

Equipment such as water boiler, electric cooker, electric bulb make use of the heating effect of electric current. Electrical conductors having higher resistivity are used here. For example, a coil made up of an alloy Nichrome is used in the electric heater-cooker as a resistor, while a tungsten wire is used in an electric bulb. Because of the current, this wire gets heated (to nearly 3400 ⁰C) and emits light. The hot wire also radiates heat to a certain extent.

The unit of electric power 1W is a very small unit, hence 1000 W or 1 kW is used as a unit to measure electric power, in practice. If 1 kW power is used for 1 hour, it will mean 1kW × 1 hr of electrical energy is used (see equation 1)

1kWh = 1 kilowatt hour = 1000 W × 3600 s = 3.6 × 10⁶ Ws = 3.6 x 10⁶ J

Several times we hear or read about a building catching fire due to short circuit. Sometimes, if we switch on an equipment in our house, the electrical fuse wire melts and the electric supply shuts down. Let us discuss about the cause briefly. The home electrical connection consists of 'live', 'neutral' and 'earth' wires. The 'live' and the 'neutral' wires have potential difference of 220V. The 'earth' is connected to ground. Due to a fault in the equipment or if the plastic coating on the 'live' and the 'neutral' wires gives way, the two wires come in contact with each other and a large current flows through it producing heat. If any inflammable material (such as wood, cloth, plastic etc) exists around that place it can catch fire. Therefore, a fuse wire is used as a precautionary measure. We have learnt about fuse wire in the previous standard. As soon as high current flows in a circuit, the fuse wire melts and breaks the circuit and any mishap is avoided.

Teacher's Note

Fuse wires protect our homes from fires. Just like a safety valve in a pressure cooker, a fuse wire breaks when too much current flows.

Exam Trick

Remember: Fuse melts when current is too high. Think of it like a weak link in a chain that breaks first to save the whole chain.

Points To Remember

A fuse wire melts when current becomes too high.
Short circuits happen when live and neutral wires touch.
Short circuits can cause fire in buildings.
Fuse wires protect electrical equipment from damage.
Earth wires are connected to the ground for safety.

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