We have provided you with Extra and Important Questions from Class 10 Science Chapter 12 Electricity. This Extra and Important Questions will help you to score 100% in your Board Exams. These extra questions will be helpful to revise the important topics and concepts.

Electricity Class 10 Important Questions with Answers Science Chapter 12

Extra Questions for Class 10 Science Chapter 12 Very Short Answer Type

Question: Write S.I. unit of resistivity.

Answer: Ohm-metre (Ωm).

Question: Name a device that helps to maintain a potential difference across a conductor.

Answer: Cell or battery

Question: Write relation between heat energy produced in a conductor when a potential difference V is applied across its terminals and a current I flows through for ‘t’.

Answer: Heat produced, H = VIt

Question: State difference between the wire used in the element of an electric heater and in a fuse wire.

Answer: The wire used in the element of electric heater has a high resistivity and have a high melting point, i.e. even at a high temperature element do not burn while fuse wire have a low melting point and high resistivity.

Question: How is an ammeter connected in a circuit to measure current flowing through it?

Answer: In series.

Question: What happens to resistance of a conductor when its area of cross-section is increased?

Answer: Resistance decreases as R∝1/A

Question: Two resistors of 10 Ω and 15 Ω are connected in series to a battery of 6 V. How can the values of current passing through them be compared?

Answer: In series, same current flows through each resistor. So, ratio of current is 1:1.

Question: Define 1 Volt.

Answer: One volt/volt: The SI unit of potential difference is volt (V). One volt is the potential difference between two points in an electric circuit when one joule of work is done to move a charge of one coulomb from one point to the other.

Question: What are resistors? Give some examples.

Answer: Substances having comparatively high electrical resistance are called resistors. Some examples of resistors are alloys like nichrome, manganin, constantan, etc.

Question: If the current passing through a conductor is doubled, what will be the change in the heat produced?

Answer: Heat produced will increase by four times (H ∝ I²)

Question: Why is an electric bulb filled with argon and nitrogen gas?

Answer: An electric bulb is filled with argon and nitrogen gas because they do not react with the hot tungsten filament and hence, prolong the life of the filament of the electric bulb.

Question: How much work is done in moving a charge of magnitude 3 C across two points having a potential difference of 12 V?

Answer:

Given : Q = 3 C, V = 12 V

To find: W

V = W/Q

W = VQ = 12 × 3 = 36 J

Question: An electric current of 4.0 A flows through a 12 Ω resistor. What is the rate at which heat energy is produced in the resistor?

Answer:

Given: I = 4 A, R = 12 Ω

Rate of production of heat energy, P = I²R = 42 × 12 = 192 W.

Question: Calculate the energy transferred by a 5 A current flowing through a resistor of 2 Ω for 30 minutes.

Answer: Here, I = 5 A, R = 2 Ω, t = 30 min = 1800 s

Energy transferred = I²Rt = (5)² × 2 × 1800 = 9 × 10⁴ J.

Question: What does the slope of V – I graph at any point represent?

Answer: Resistance.

Extra Questions for Class 10 Science Chapter 12 Short Answer Type

Question: Sketch a circuit diagram of an electric circuit consisting of a cell, an electric bulb, an ammeter, a voltmeter and a plug key.

Answer:

Question: Differentiate between Resistance and Resistivity.

Answer:

Resistance:

1. It is the opposition provided by the atoms of a conductor to the flow of electrons.
2. SI unit of resistance is Ω (Ohm).
3. Resistance depends on length, area of cross section, material and temperature of conductor.

Resistivity:

1. It is the resistance of the conductor of that substance of unit length and unit area of cross section.
2. SI unit of Resistivity of Ωm (Ohm-meter).
3. Resistivity of substance depends only on the material of substance.

Question: Nichrome wire is used for making the Ideating elements of electrical appliances like iron, geyser, etc. Give reasons.

Answer:

Nichrome wire is used for making the heating elements of electrical appliances like iron, geyser, etc. because:

• Nichrome has a very high resistance due to which it produces a lot of heat on passing current.
• It does not undergo oxidation easily even at high temperature due to which it can be kept red hot.

Question: What is an electric circuit? Distinguish between an open and a closed circuit.

Answer: Electric circuit: A continuous and closed path of electric current is called an electric circuit.

Open circuit: A discontinuous circuit through which no current can flow.

Closed circuit: A circuit without interruption, providing a continuous path through which a current can flow.

Question: What is the better way of connecting lights and other electrical appliances in domestic wiring? Why?

Answer: The better way of connecting lights and other electrical appliances in domestic wiring is parallel connection because of the following advantages:

• In parallel circuit, if one appliance stops working due to some defect, then all other appliances keep working normally.
• In parallel circuit, each electrical appliance has its own switch due to which it can be turned on or off, without affecting other appliances.
• In parallel circuit, each electrical appliance gets the same voltage (220 V) as that of the power supply line.
• In parallel circuit, the overall resistance of the domestic circuit is reduced due to which the current from the power supply is high.

Question: An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to aft V battery (Fig.).Calculate (a) the total resistance of the circuit, (b) the current through the circuit, and (c) the potential difference across the electric conductor.

Answer: (a) Resistance of electric lamp, R₁ = 20 W

Resistance of series conductor, R_² = 4 W

Total resistance in the circuit,Rs = R₁ + R_² = 20 Ω + 4 Ω = 24 Ω.

(b) Total potential difference, V = 6 V

By Ohm’s law, the current through the circuit is

(c) Potential difference across the electric lamp,

V_¹ = IR_¹ = 0.25 A × 20 Ω = 5 V.

Potential difference across the conductor is

V_² = IR_² = 0.25 A × 4 Ω = 1 V.

Question: A wire has a resistance of 10Ω. It is melted and drawn into a wire of half of its length. Calculate the resistance of the new wire. What is the percentage change in its resistance?

Answer: Given: R_¹ = 10 Ω, l_² = l_¹/2

To find: (a) R_²

(b) Percentage change in the resistance (ΔR%).

If volume of the wire remains same in both the cases.

Question : Two lamps, one rated 60 W at 220 V and other 40 W a 220 V, are connected in parallel to an electric supply at 220 V. [CBSE 2016]

(a) Draw the circuit diagram to show the connections.

(b) Calculate the current drawn from the electric supply.

(c) Calculate the total energy consumed by the two lamp together when they operate for one hour.

Answer: (a) The required circuit diagram is shown below:

(b) Total power of the two lamps = 60 + 40 = 100 W

Applied Voltage, V = 220 V

Current drawn from the electric supply,

(c) Total energy consumed by the lamp in one hour = 60W × 1h + 40W × 1h = 100 Wh = 0.1 kWh.

Question: A 9Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination.

Question: (a) What do the following circuit symbols represent?

(b) The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. Find the resistance of heater when in use.

Answer: (a) (i) Wires crossing without touching each other. (ii) Rheostat/Variable resistor

(b) Given: V = 60 V, I = 4 A, R = ?

From Ohm’s law, V = IR⇒ 60 = 4 × R

⇒ R = 15 Ω

Question: The charge possessed by an electron is 1.6 × 10-19 coulombs. Find the number of electrons that will flow per second to constitute a current of 1 ampere.

Question: The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating of the filament in the two cases).

Extra Questions for Class 10 Science Chapter 12 Long Answer Type

Question: V-I graph for two wires A and B are shown in the figure. If both wires are of same length and same thickness, which of the two is made of a material of high resistivity? Give justification for your answer.

Answer: Greater than slope of V-I graph, greater will be the resistance of given metallic wire. In the given graph, wire A has greater slope then B. Hence, wire A has greater resistance.

For the wires of same length and same thickness, resistance depends on the nature of material of the wire, i.e.,

Hence, wire ‘A’ is made of a material of high resistivity

Question: Two identical wires one of nichrome and other of copper are connected in series and a current (I) is passed through them. State the change observed in the temperatures of the two wires. Justify your answer. State the law which explains the above observation.

Answer: The resistivity of nichrome is more than that of copper so its resistance is also high. Therefore, large amount of heat is produced in the nichrome wire for the same current as compared to that of copper wire. Accordingly, more change in temperature is observed in the nichrome wire. This is explained by Joule’s law of heating.

Joule’s law of heating: It states that the amount of heat produced in a conductor is

• directly proportional to the square of current flowing through it, i.e., H ∝ I²
• directly proportional to the resistance offered by the conductor to the current, ie., H ∝ R
• directly proportional to the time for which current is flowing through it, i.e.,H ∝ t

Combining these, we get

H ∝ I²Rt⇒ H = KI²Rt

Where K is proportionality constant and in SI system, it is equal to one.

Question: An electric bulb is rated at 60 W, 240 V. Calculate its resistance. If the voltage drops to 192 V, calculate the power consumed and the current drawn by the bulb. (Assume that the resistance of the bulb remain unchanged.)

Question: Series arrangements are not used for domestic circuits. List any three reasons.

Answer: Series arrangements are not used for domestic circuit because

• The electrical appliances need current of widely different values to operate properly.
• In series arrangement, when one component fails, the circuit is broken and none of the components works.All electrical appliances work at a constant voltage.
• But in series circuit, the current is constant throughout the electric circuit and potential is different across the different components. So, series arrangement is not suitable for domestic circuits.

Question: Name the physical quantity which is (i) same (ii) different in all the bulbs when three bulbs of:

(a) same wattage are connected in series.

(b) same wattage are connected in parallel.

(c) different wattage are connected in series.

(d) different wattage are connected in parallel.

Answer: (a) For identical bulbs in series- same current, same potential difference.

(b) For identical bulbs in parallel- same potential difference, different current.

(c) For unidentical bulbs in series- same current, different potential difference.

(d) For unidentical bulbs in parallel- different current, same potential difference

Question: Two devices of rating 44 W, 220 V and 11 W, 220 V are connected in series. The combination is connected across a 440V mains. The fuse of which of the two devices is likely to burn when the switch is ON? Justify your answer.

Question: Two resistors with resistances 5Ω and 10 Ω are to be connected to a battery of emf 6 V so as to obtain:

(i) minimum current (ii) maximum current

(a) How will you connect the resistances in each case?

(b) Calculate the strength of the total current in the circuit in the two cases.

Answer: (a) As current is inversely proportional to resistance for the same voltage. So, to get maximum current, the equivalent resistance has to be less. This means the resistors must be connected in parallel. To get minimum current, the equivalent resistance has to be greater as I∝1/R. This means the resistors must be connected in series.

Question: You are given three resistors of 10 Ω, 10 Ω, 20 Ω to a battery of emf 2.5 V, a key, an ammeter and a voltmeter. Draw a circuit diagram showing the correct connections of given components such that the voltmeter gives a reading of 2.0 V.

Answer:

Question: The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below:

Plot a graph between V and I and calculate the resistance of the resistor.

Answer: The graph between V and I for the given data is shown below: