CBSE PHYSICS By JSUNIL

When charge (electron) move through conductor ,collide with atoms of the conductors due to resistance and transfer energy to the conductor which appear as heat .

Electrical Power:

The rate of doing work in moving charge through conductors

We know that P = H/t Þ H = Pt

**Heating Effect of Electric Current**When charge (electron) move through conductor ,collide with atoms of the conductors due to resistance and transfer energy to the conductor which appear as heat .

Hence work done by electron to overcome resistance is equal
to heat generated in conductors.

Let W work done to move Q charge through a conductor of
resistance R that appear as Heat

**W = H**

But , V = W/Q Þ
W = Q V

Þ H = QV

But, I = Q /t Þ Q = It

**\**

**H = V I t**

Also, V = IR

Þ H = It
x IR

Þ H =I

^{2}RtElectrical Power:

The rate of doing work in moving charge through conductors

OR, The rate of producing heat in conductor

Or, Rate of producing electrical Energy

P = W/ t

OR, P = H/t

But, H =I

^{2}Rt
P = I

^{2}Rt /t Þ P = I^{2}R
Also we may
express Power as

P = I x I x R

Using V =IR

**P = VI**

SI unit of
POWER

P = H/t =
1J/1Sec = Watt

If 1oule
energy consumed by device in 1 sec Its power said to be 1 watt

**Commercial electrical Energy unit is kWh**

We know that P = H/t Þ H = Pt

If 1 kW (1000watt)
energy consumed for 1 hour It is called 1unit(BOT unit)

**Energy in term of joule:**

H = 1kWh = 1000W x 3600sec =1000J/sec x 3600sec = 3.6 x
10

^{6}j
Q. 1. Find
the work done by an electron to maintain the potential difference of 80V?

Q. 2. What is the potential difference between the ends of 16Ω resistance, when a current of 1.5A flows through it?

Q. 3. The potential difference across the the terminals of an electric iron is 240V and the current is 6 A what is the resistance of electric iron?

Q. 4. If there are 108 electrons flowing across any cross section of a wire in 4 minutes, what is the current in the wire?

Q. 5. .A copper wire has diameter o.5mm and resistivity 1.6 x 10-8 ohm m what will be the length of this wire to make the resistance of 10 ohms?

Q. 6. Find the effective resistance of resistors 0.01 ohms and 107 ohms.in series and parallel

Q. 7. Two resistors of same materials has been connected in series first and then in parallel. Draw a V – I graph to distinguish these connection.

Q. 8. Three resistors 3,4,5 ohms are joined in parallel in a circuit. If a current of 150 mA=150×10-3A flows through the resistor of 4 ohms, then find the values of the current in mA which will be flowing in other two resistors?

Q. 9. A wire of length 2cm having resistance R is stretched to have an increase of 100% of original length . Find its new resistance with respect to its original resistance.

Q. 10. An electric lamp has resistance of 400 ohms. It is connected to a supply of 250V. If the price of electric energy is Rs.1.20 per unit, calculate the cost of lighting the lamp for 20 hours.

Q. 2. What is the potential difference between the ends of 16Ω resistance, when a current of 1.5A flows through it?

Q. 3. The potential difference across the the terminals of an electric iron is 240V and the current is 6 A what is the resistance of electric iron?

Q. 4. If there are 108 electrons flowing across any cross section of a wire in 4 minutes, what is the current in the wire?

Q. 5. .A copper wire has diameter o.5mm and resistivity 1.6 x 10-8 ohm m what will be the length of this wire to make the resistance of 10 ohms?

Q. 6. Find the effective resistance of resistors 0.01 ohms and 107 ohms.in series and parallel

Q. 7. Two resistors of same materials has been connected in series first and then in parallel. Draw a V – I graph to distinguish these connection.

Q. 8. Three resistors 3,4,5 ohms are joined in parallel in a circuit. If a current of 150 mA=150×10-3A flows through the resistor of 4 ohms, then find the values of the current in mA which will be flowing in other two resistors?

Q. 9. A wire of length 2cm having resistance R is stretched to have an increase of 100% of original length . Find its new resistance with respect to its original resistance.

Q. 10. An electric lamp has resistance of 400 ohms. It is connected to a supply of 250V. If the price of electric energy is Rs.1.20 per unit, calculate the cost of lighting the lamp for 20 hours.

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