# Class 10 Science|physics Important Questions for Electricity

Given below are the Class 10 Science Important Questions for electricity
(a) Very Short Answer Based questions
(b) Match the column
(c) Table type question

## Very Short Answer Based questions

1. What is relation between KWH and Joule?
2. The Flow of electron constitutes the electric current in the wire.  True or false?
3. A voltmeter has high resistance and it is connected in parallel  True of false?
4. What is resistance of the conductor?
5. What is the SI unit of resistivity?
6. What are the applications of chemical effect of current?
7. What is same across the parallel combination of resistors Voltage or current?
8. What is critical temperature in metals?

1. $1 \; KWH = 3.6 \times 10^6 \; Joule$
2. True
3. True
4. Electric resistance is the ratio of potential difference across the two ends of conductor and amount of current flowing through the conductor.
5. The SI unit of resistivity is Ω m
6. Heater, bulb
7. Voltage
8. The temperature at which the resistance falls to zero is called Critical Temperature.

a- > ii
b -> i, v
c -> iv
d -> iii
e -> iii
f -> iv

## Table type question

Two heaters A and B are given

Some more questions to be answered based on above data
1. Which Heater for high resistance
2. If 1KWH is priced at 30 paise,which heater  will be turned costlier if they run for 1 hours each

i. Heater A has higher resistance
ii.
Heater A
$E= P \times t =150 \times 1 = .15 KWH$
Heater B
$E= P \times t =100 \times 1 = .10 KWH$
So heater A will be costly

Question 1.
What happens to resistance when length of conductor is doubled without affecting the thickness of conductor?

$R = \rho \frac {L}{ A }$
So,Resistance will be doubled

Question 2.
What is the lowest resistance that can be obtained by combining four coils of resistors of 4 Ω, 8 Ω, 12 Ω and 24 Ω?

$\frac {1}{R}= \frac {1}{4} + \frac {1}{8} + \frac {1}{12} + \frac {1}{24}$
$R=2$ ohms
So,Resistance will be doubled

Question 3.
What is an ammeter?
Question 4.
Calculate the number of electrons constituting one coulomb of charge.

$n = 6.2 \times {10^{18}}$ electrons

Question 5.
A voltmeter is to be connected in the circuit to measure potential difference across a conductor. Mention the type of combination in which it should be conducted with the conductor.
Question 6.
A bulb cannot be used in place of a resistor to verify Ohm’s law. Justify this statement with reason.
Question 7.
What is meant by electric resistance of a conductor?
Question 8.
Define resistance of a conductor.
Question 9.
Write SI unit of resistivity.
Question 10.
How does the resistivity of alloys compare with those of pure metals form which they may have formed?
Question 11.
Mention any two factors on which the resistance of a cylindrical conductor depends.
Question 12.
Write the relation between resistance R of filament of a bulb, its power (P) and a constant voltage V applied across it.

$P=\frac {V^2}{R}$

Question 13.
Power of a lamp is 100 W. Find the energy in joules consumed by it in 1 s.

100 J

Question 14.
When a 12 V battery is connected across an unknown resistor, 2.5 mA current flows in the circuit. Find the resistance of the resistor.

4800 Ω

Question 15.
State the factors on which the resistance of a cylindrical conductor depends. Hence, define resistivity.
Question 16.
In an electric circuit with a resistance wire and a cell, the current flowing is I. What would happen to this current if the wire is replaced by another thicker wire of same material and same length. Give reason.

$R = \rho \frac {L}{ A }$
So,Resistance will be decrease with thick wire
Now I=V/R ,so current will increase

Question 17.
A wire of length L and resistance R is stretched so that the length is doubled and area of cross – section halved. How will
(i) resistance change, and
(ii) resistivity change.

$R = \rho \frac {L}{ A }$
(i) So resistance will becomes four time
(ii) resistivity will remain same
Now I=V/R ,so current will increase

Question 18.
(a) What material is used in making the filament of an electric bulb?
(b) Name the characteristics which make it suitable for this.
Question 19.
An electric lamp is marked 220 V, 100W. It is used for 5 hours daily. Calculate:
(a) Its resistance while glowing.
(b) Energy consumed in kW h/day.

(a) 484 Ω
(b) 0.5 kW h

Question 20.
List in a tabular form two differences between a voltmeter and an ammeter.
Question 21.
A thick wire and a thin wire the same material are successively connected to the same circuit to find their respective resistance. Which one will have lower resistance? Give reason.
Question 22.
State the factors on which the heat produced in a current carrying conductor depends. Give one practical application of this effect.
Question 23.
Write the relation between electric power (W) of a device with potential difference (Volt) across it and current (I) flowing through it.

$P=VI$

Question 24.
What is electrical resistivity? In a series circuit comprising of a resistor having a metallic wire, the ammeter reads 5 A. The reading of the ammeter decrease to half when the length of the wire is doubled. Why?

Question 1.
Draw the symbols of commonly used components in electric circuit diagrams for:
(i) An electric cell
(ii) open plug key
(iii) Wires crossing without connection or joining
(iv) Variable resistor
(v) Battery
(vi) Electric bulb
(vii) Resistance
(viii) Wire joint

Question 2.
Draw a labeled circuit diagram to study a relationship between the current (I) flowing through a conductor and the potential difference (V) applied across its two ends. State the formula correlating the I in a conductor and the V across it. also show this relationship by drawing a diagram.
Question 3.
In electric potential difference a scalar or vector quantity? What do you mean by a potential difference of 1 volt?

Ilectric potential difference is a scalar quantity as it has only magnitude with no direction
The potential difference between two points is said to be one Volt if 1 Joule of work is done in moving 1 Coulomb of electric charge from one point to another.

Question 4.
a. What does an electric circuit mean?
b. Name a device that helps to maintain a potential difference across a conductor in a circuit.
c. When do we say that the potential difference across a conductor is 1 volt?
d.Calculate the amount of work done in shifting a charge of 2 coulombs from a point A to B having potentials 10 V and 5V respectively.

a.Electric circuit is a continuous path consisting of cell (or a battery), a plug key, electrical component(s), and connecting wires in which current flows.
b. Electric cell or battery
c.The potential difference between two points is said to be one Volt if 1 Joule of work is done in moving 1 Coulomb of electric charge from one point to another.
d. Work done = qV where V is Potential difference
V= 10-5= 5 V, q= 2C
Workdone = $2 \times 10 = 10$ J

Question 5.
State Ohm's law. How can it be verified experimentally? Does it hold good in all conditions? Comment.
Question 6.
Express Joule's law of heating mathematically.
Question 7.
What is the resistance of 12 m wire having radius 2×10-4 m and resistivity 3.14×10-8 Ω-m.

$R=\rho \frac {L}{A}$
Substituting all the values , we get
R=3Ω

Question 6.
A 4Ω resistance wire is doubled on it. Calculate the new resistance of the wire.

Here we consider wire doubled means to fold the length of wire. It means its length will get half and area of cross section will get double. Let the resistance of the wire originally 'R' of length 'l' and area of cross-section 'A' with resistivity of material is 'ρ', Then
$R=\rho \frac {L}{A} =4$
When it is doubled, L1=L/2, A1=2A ,then
$R_1=\rho \frac {L/2}{2A} =\frac{1}{4} \rho \frac {L}{A}$ =1Ω

Question 7.
a.Define 1 volt. Express it in terms of SI unit of work and charge.
b. Calculate the amount of energy consumed in carrying a charge of 1 coulomb through a battery of 3 volts.

a. One volt is defined as the the potential difference between two points in a current carrying conductor when one joule of work is done to move a charge of one coulomb from one point to another.
SI unit in terms of work and charge
1 volt= 1 joule / 1 coulomb

b. Q= 1 C ,V= 3 Volt
Workdone is given by
W = Q V = 3 Joule

Question 8.
The resistance per meter length of a wire is 10 Ω. If the resistivity of the material of the wire is 50×10-8 ohm meters, find the area of cross – section of the wire.

R=10 Ω , ρ=50×10-8 ohm meters, L=1m
$R=\rho \frac {L}{A}$
$A=\rho \frac {L}{R}$
A=50×10-9 m2

Question 9.
When a resistor R is connected to a battery of 3 V, it draws a current of 1 ampere. find the value of R. If an identical resistor is connected in parallel with it, find the current that flows through the circuit?.

By ohm law
$V=IR$
or $R = \frac {V}{I} = 3$Ω

Now when identical resistor is connected in parallel with it, effective resistance becomes
$\frac {1}{R_{eq}}= \frac {1}{3} + \frac {1}{3}$
or $R_{eq}= 1.5$ Ω
Now
$I = \frac {V}{R} = \frac {3}{1.5} =2 A$

Question 10.
Derive an expression for the equivalent resistance of three resistors R1, R2 and R3 connected in parallel.

• Resistance of a system of resistors

• Question 11.
Christmas tree lamps are usually connected in series. What will be if one lamp breaks?

Since they are connected in series if one of the lamp is broken, circuit will become incomplete and no electric current will flow . Hence lamp will not glow

Question 12.
With the help of a neat diagram derive the expression for the effective resistance when three resistors R1, R2 and R3 are connected is series.

• Resistance of a system of resistors

• Question 13.
What would be the resistance of a resistor if the current flowing through it is 0.15 A when the potential difference across it is 1.05 V?

R= V/I = 1.05/.15 =7 Ω

Question 14.
(a) Name and state the law that gives relationship between the potential difference (V) across the two ends of a conductor and the current (I) flowing through it.
(b) Represent it (Ohm's law) mathematically.
(c) Draw a circuit diagram for the verification of Ohm's law.
(d) Draw the V - I graph for this (Ohm's) law.

Question 15.
State and explain Ohm's law. Define resistance and give its SI unit. What is meant by 1 ohm resistance? Draw V - I graph for an ohmic conductor and list its two important features.

Question 16.
What is meant by resistance of a conductor? Name and define its SI unit. List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected if:
(i) its length is doubled

Electric resistance of a conductor is the obstruction offered by the conductor to the flow of the current through it. SI unit of resistance is Ohm (O) where 1 Ohm=1 volt/1 Ampere

The resistance of the conductor depends
i.on its length
ii.on its area of cross-section
iii.on the nature of its material

Resistance is given as
$R = \rho \frac {L}{A}$
So if Lenght is doubled ,Resistance is doubled
If radius is doubled , Resistance is one -fourth

Question 17.
List two distinguishing features between the resistance and resistivity of a conductor. A wire is stretched so that its length becomes 6/5 times of its original length. If its original resistance is 25 Ω find its new resistance. Give justification for your answer in each case.

Resistance of a conductor of length L and an area of uniform cross section is
$R = \rho \frac {L}{ A }$
Given R = 25 Ω

Let us assume that the density of the material remains the same. Hence the volume of the conductor remains the same.
$A L = A_1 L_1$
$A_1 = \frac {A L }{L_1}$

After stretching the wire $L_1 = \frac {6 L}{ 5}$
$A_1 = \frac {5 A L }{ 6 L} = \frac {5 A }{ 6}$

Resistance of stretched wire
$R_1 = \rho \frac {L_1 }{A_1}$
$= \rho \frac { 6 L /5}{5 A/6}$
$=\frac {36}{25} \rho \frac { L}{A}$
$= \frac {36}{25} \times 25=36$ Ω