Electricity — Class 10 Science PYQs

For Questions number 8 and 9, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.
(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.
Assertion (A): There are generally a greater number of individuals at the lower trophic levels of an ecosystem.
Reason (R) : The greatest number is of the producers.

The correct way to connect an ammeter and a voltmeter in an electric circuit is :

Work done in displacing an electron between two points having potential difference of $\text{1 V}$, is :

(a) Define volt, the unit of potential difference.
(b) Calculate the work done required to move an electron between two points A and B located at a potential difference of $100\,\text{V}$ in an electric field.

In an electric circuit carrying current $I$, a $$\begin{aligned}& 2 \\ & \Omega\end{aligned}$$ resistor is replaced by an $$\begin{aligned}& 8 \\ & \Omega\end{aligned}$$ resistor without changing the connected (ideal) battery. Then :

(a) The resistance of a wire of $$\begin{aligned}& 0.01 \\ & \text{cm}\end{aligned}$$ radius and $$\begin{aligned}& 1.0 \\ & \text{cm}\end{aligned}$$ length is $$\begin{aligned}& 7 \\ & \Omega\end{aligned}$$. Calculate its resistivity.

Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire.
Shweta put nichrome wire of length ‘l’ in the circuit and after plugging the key, noted current in the ammeter.
Ayesha put nichrome wire of same thickness but twice the length i.e. ‘2l’ in the circuit and after plugging the key, noted current in the ammeter.
Samridhi took copper wire of length ‘l’ and same thickness in the circuit and after plugging the key, noted current in the ammeter.
(a) If the ammeter reading is X ampere with nichrome wire of length ‘l’, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?
(b) What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ‘l’ the same ?
(c) Define ‘resistivity’. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.

(a) (i) Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why?
(ii) Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?
(iii) Define the S.I. unit of electric current.

(B) (i) Define electrical resistivity of a material.
(ii) How will the resistivity and resistance of a conducting wire change if the length and area of cross-section of wire both are doubled? Justify your answer.
(iii) Calculate the electric current flowing through a $$\begin{aligned}& 4 \\ & \Omega\end{aligned}$$ resistor that produces $$\begin{aligned}& 100 \\ & \text{J}\end{aligned}$$ of heat every second.

Attempt either subpart (a) or (b) :
OR
(b) (i) State the relationship of the resistance (R) of a wire with its area of cross-section (A) and its length (l). With the help of this relation, define resistivity of the material of the wire.
(ii) In an electric circuit, $\text{2 A}$ electric current flows through a $\text{40 \Omega}$ resistor for $\text{50}$ seconds. (I) Calculate the heat produced in the wire. (II) If another $\text{40 \Omega}$ resistor is connected in parallel to the given $\text{40 \Omega}$ resistor, calculate the heat produced in the circuit in $\text{50}$ seconds.

(b) (i) How many bulbs of resistance $$\begin{aligned}& 8 \\ & \Omega\end{aligned}$$ each should be connected in parallel combination to draw a current of $$\begin{aligned}& 2 \\ & \text{A}\end{aligned}$$ from a battery of $$\begin{aligned}& 4 \\ & \text{V}\end{aligned}$$?
(ii) Name the device used for measuring electric current. How is it connected in a circuit ?
(iii) State Joule's law of heating.

Read the following passage and answer the questions that follow :
Swati, a class 10 student, observes that when she passes close to the refrigerator in her kitchen, she feels the heat, although the things kept inside the refrigerator are cool.
Describe the cause of heating in the above-mentioned case.

A current $\text{I}$ flows through a resistor of resistance $\text{R}$ when the potential difference across it is $\text{V}$. Applying Ohm's law, write the formula for amount of heat produced by the resistor in time $\text{t}$.

Read the following passage and answer the questions that follow :
Swati, a class 10 student, observes that when she passes close to the refrigerator in her kitchen, she feels the heat, although the things kept inside the refrigerator are cool.
(a) Describe the cause of heating in the above-mentioned case.

Write any two practical applications of heating effect of electric current.

(a) Name a device which is used to :
(i) Maintain a constant potential difference in a circuit.
(ii) Change the electric current in an electric circuit.
(b) When the potential difference between the terminals of an electric heater is $$\begin{aligned}& 110 \\ & \text{V}\end{aligned}$$, a current of $$\begin{aligned}& 5 \\ & \text{A}\end{aligned}$$ flows through it. What will be the value of current flowing through it when the potential difference is increased to $$\begin{aligned}& 220 \\ & \text{V}\end{aligned}$$ ?

Read the following passage and answer the questions that follow :
Swati, a class 10 student, observes that when she passes close to the refrigerator in her kitchen, she feels the heat, although the things kept inside the refrigerator are cool.
(a) Describe the cause of heating in the above-mentioned case.
(b) A current $\text{I}$ flows through a resistor of resistance $\text{R}$ when the potential difference across it is $\text{V}$. Applying Ohm's law, write the formula for amount of heat produced by the resistor in time $\text{t}$.
(c) (i) Write any two practical applications of heating effect of electric current.
OR
(c) (ii) Define the commercial unit of electric energy and express it in Joules (J).

(b) An electric heater is rated $$\begin{aligned}& 220 \\ & \text{V}\end{aligned}$$; $$\begin{aligned}& 11 \\ & \text{A}\end{aligned}$$. Calculate the power consumed if the heater is operated at $$\begin{aligned}& 200 \\ & \text{V}\end{aligned}$$.

Define the commercial unit of electric energy and express it in Joules (J).

(i) How much electric current will an electric iron draw from $220\,\text{V}$ source if the resistance of its heating element when hot, is $55\,\Omega$ ? Calculate the power consumed by the electric iron when it is operated at $220\,\text{V}$.
(ii) In a house, 3 bulbs of $100\,\text{watt}$ each, are lit for $5\,\text{hours}$ daily and an electric heater of $1.0\,\text{kW}$ is used for half an hour daily. Calculate the total energy consumed in a month of $30\,\text{days}$ and its cost at the rate of ₹ $3.60$ per $\text{kWh}$.
(iii) With reason explain, why are alloys commonly used to make elements of electrical heating devices.

(i) Define the SI unit of power. Express the electric power of an electric appliance in terms of potential difference and current flowing through it.
(ii) In a house, 3 bulbs of $100\text{ W}$ each, are lit for $5\text{ hours}$ daily and an electric heater of $1.0\text{ kW}$ is used for half an hour daily. Calculate the total energy consumed in a month of 30 days and its cost at the rate of ₹ $3.60$ per $\text{kWh}$.
(iii) Convert the commercial unit of electric energy into Joule (J).

Attempt either subpart (a) or (b) :
(a) (i) In a house, $\text{5}$ fans, rated $\text{100 W}$; $\text{220 V}$ each are used for $\text{4}$ hours daily and an electric heater rated $\text{1000 W}$; $\text{220 V}$ is used for $\text{5}$ hours daily. Calculate the cost of electrical energy consumed by the fans and the electric heater in a month of $\text{30}$ days if the cost of $\text{1}$ unit of electrical energy is $\text{\text{Rs}5}$.
(ii) You have two fuse wires X and Y with electric current rating $\text{5 A}$ and $\text{10 A}$ respectively. Which of the two would you use with a heater rated $\text{2000 W}$; $\text{220 V}$ ? Justify your answer.