CBSE : Class X : Science : Chapter 12 : Electricity : Question And Answer
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 Published date: December 9, 2018
 Modified date: December 9, 2018

 Vasai East, Thane, Maharashtra
Q 1: Important Definitions :
Ans:
* Electricity : The flow of charge through conductor is called electric current.
* Electric Circuit : A continuous and closed path of an electric current is called an electric circuit.
* Current : Electric current is number of charges flowing through any crosssectional area in one second.
* Ampere : Ampere is the unit of current and is defined as One ampere is constituted by the flow of one coulomb of charge per second.
* Potential Difference : The work done to move 1 C charge from one end to the other end of the conductor is called potential difference. It is denoted by letter `V` (Volt).
*Ammeter : It is an instrument to measure current in a conductor. It is always connected in series in a circuit.
* Voltmeter : It is an instrument use to measure potential difference between two end of a conductor. It is always connected in parallel.
* Ohm's Law : According to ohm's law, the current flowing through a conductor is directly proportional to the potential difference applied across the end of the conductor provided the physical conditions remain the same.
* Resistance : It is the property that resist the flow of electrons in a conductor. it controls the magnitude of the current and its unit id ohm.
* 1 Ohm : The resistance of a conductor is said to be 1 ohm if 1 ampere of current flows through it when the potential difference across the end is one volt. * Electric Power : It is the electric energy consumed in one second. The unit is watt.
* 1 Watt : When an electrical appliance consume electrical energy at the rate of 1 Joule/sec, its power is said to be 1 watt.
* Electrical Energy : The electrical energy consumption by an appliance is given by product of the power rating and time for which it is used.
* 1 Watt hour : 1 watt is the amount of electrical energy consumed when an electrical appliance of 1 watt power is used for 1 hour.
* 1 KiloWattHour: 1 KiloWattHour means the amount of energy consumed when an electrical appliances of 1000 watt is used for 1 hour.
* Joules Law of heating effect : Joules law of heating effect states that when a current pass through a resistance for a time 't; , the heat produced will be directly proportional to the square of the current, resistance and time.
Q2: What is Ohm's Law ? Explain with diagram ?
Ans: Ohm’s Law : According to Ohm’s Law, the current flowing through a conductor is directly proportional to the potential difference applied across the end of the conductor provided the physical condition remain same.
Mathematically
V ∝ I wher V is Voltage and I is current
V=IR
where R is the proportionality constant called resistance of conductor.
SI unit of resistance is ohm and is denoted by symbol (Ω )
Q3: Name the factor which affects the resistance ?
Ans : Resistance plays a significant role in flow of current through a conductor. Following are the factors affecting resistance:
a) Length of the conductor :
The resistance of a conductor is directly proportional to the length of the conductor.
R ∝ l wher R is Resistance and l is length of conductor
b) Area of crosssection:
The resistance of a conductor is inversaly proportional to the area of crosssection.
R ∝ 1 / A
∵ R ∝ l
∴ R= ρ l/A
where rho (ρ) is called the resistivity or the specific resistance of conductor
c) Material of the conductor :
Two conductor of same length and are of same area of crosssection will show different resistance if they are of different materials with high value of resistivity will have high reistance and vice versa.
d) Temperature : With the rise of temperature the resistance of the metal increases and vice versa.
Q4: What are the various combination through which resistance are connected in electric circuit ?
Ans : Following are the various combination through which resistance can be connected in electric circuit :
1) Resistance in Series : When the number of resistance are connected end to end so that same current flows through each resister, then the resisters are said to be connected in series.
In Fig 1. the resistance R_{1} , R_{2}, R_{3 } are connected in series across a cell of potential difference V. When a current flows through a resistance, a potential drop occurs across the resistance by ohms law.
The potential difference across R_{1} is
V_{1} = IR_{1}
Similarly, V_{2} = IR_{2 }
V_{3} = IR_{3}
the potential difference V = V_{1} + V_{2}+ V_{3}
so V = IR_{1} + IR_{2}+ IR_{3}
V = I ( R_{1} + R_{2}+ R_{3})  (1)
Let R_{s }be the equivalent resistance offered by the three resistance R_{1} , R_{2}, R_{3 }connected in series , then potential difference
V = IRs  (2)
From equation (1) & (2)
IRs = I ( R_{1} + R_{2}+ R_{3})
or Rs = R_{1} + R_{2}+ R_{3}
2) Resistance in Parallel :
In fig 2. three resistance R_{1} , R_{2}, R_{3 }connected in parallel to one another between two points. A battery of "V" volt has been applied across this combination. In this case potential difference across all the 3 resistance will be the same. The current passing through this resistances connected in parallel is not same.
Let the total current be I then the current through the resistance R_{1} will be I_{1} ,R_{2} will be I_{2} and through R_{3} will be I_{3}
so total current I = I_{1 }+ I_{2} + I_{3}
By ohms Law V = I/R
I_{1 =}V/R_{1}
I_{2} = V/R_{2}
I_{3 = }V/R_{3}
Substitute the value of I_{1 ,} I_{2 ,} I_{3 }in the equation I = I_{1 }+ I_{2} + I_{3}
V/R = V/R_{1}+ V/R_{2} + V/R_{3}
V/R = V(1/R_{1} + 1/R_{2} + 1/R3 )
1/R_{p} = 1/R_{1} + 1/R_{2} + 1/R_{3}
Where R_{p} is equivalent resistance when the three resistance are connected in parallel.
Q 5: Define Joules law of heating effect.
Ans :  Joules law of heating effect states that when a current passes through a resistor for a time 't', the heat produced will be directly proportional to the square of the current, resistance and time.
H ∝ I²
H ∝ R
H ∝ t
Q6: Explain heating effect of of electric current with mathematical expression.
Ans : When an electric current is passed through a high resistance wire like Nichrome, the resistance becomes very hot and produce heat energy. This effect is known as heating effect of electric current.
When an electric charge Q moves against potential difference V, the amount of work done is equal to
W = V x Q  (1)
From definition of current
I = Q / T
or Q = I x T ( 2)
from (1) & (2)
W = V x I x T
ie W = VIT
by Ohms Law
V = IR
W = IR x IT
ie W = I²RT
The work is converted to heat energy
∴ H = I²RT
Q7:What is Electric power ? Derive its mathematical expression.
Ans :  Electric power is the electrical energy consumed in one second. The unit is watt.
Power ∝ 1 / Resistance
Mathematical Expression of Electric Power :
Power = work done / time
P = W / T
as W = VQ (where V is potential difference and Q is charge)
P = VQ / T
since I = Q / T
P = V I  (1)
By Ohm's law R = V / I
V = I R
From (1) P = V I
P = I R x I
P = I² R
As P = V I
∵ I = V / R
P = V x V /R
P = V²R  Mathematical expression of Electric Power
Q8: What are the advantage of parallel circuit in domestic wiring ?
Ans : Following are advantages of parallel circuit in domestic wiring :
a) In parallel circuit if one electrical appliance stop due to some defects, all the other connected appliances will keep working normally.
b) In parallel circuit, each appliance can be turned ON/OFF without affecting other connected appliances.
c) In parallel circuit, all appliances get the same voltage
d) In parallel circuit, each appliance draws current equivalent to resistance they offer in circuit.
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