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

\$\textbf{Explanation}\$\$\bullet\$Potential difference is the difference of electrical potential between two points which is defined as the amount of work energy is required to move an electric charge from one point to another.\$\bullet\$An electric cell or battery helps to maintain a potential difference across a conductor.\$\bullet\$The cells only provide the energy required to work on the charge in order to transport it from the negative to the positive terminal. \$\bullet\$The cell can sustain an electric potential difference across the two ends of the external circuit by giving energy to the charge.

Question 1

Identify the circuit (Figure 12.3) in which the electrical components have been properly connected

Accepted Answer

Hint: Check the connections of the Voltmeter and Ammeter.Step 1: Checking if the Voltmeter is connected in parallel and Ammeter is connected in series.   In circuits $(i)$ and $(iii)$, Voltmeter is connected in series. In circuit $(iii)$ the ammeter is connected in parallel. In circuits $(i)$ and $(iii)$, connections are not proper. In circuits $(ii)$ and $(iv)$, the Voltmeter and Ammeter are connected in parallel and series respectively. Step 2: Checking if the terminals are connected properly.   In circuit $(iv)$, the positive terminal of the ammeter is connected with the negative terminal of the cell. Hence it is not proper. Whereas in circuit $(ii)$, all the terminals are properly connected. Therefore option $(B)$ is the correct option.

Question 2

What is an electromagnet? Draw a circuit diagram to show how a soft iron piece can be transformed into an electromagnet.

Accepted Answer

The magnetic field produced due to current flowing in a coil or a solenoid can be used to magnetise a material like soft iron temporarily. The insulated copper wire is warpped on a soft iron piece. When current is passed through the coil using a battery and a key the iron piece behaves like a bar magnet as long as current is being passed. Such a magnet is called an electromagnet.

Question 3

When a switch is in OFF position, i) Circuit starting from the positive terminal of the cell stops at the switch.ii) Circuit is open.iii) No current flows through it.iv) Current flows after some time.Choose the combination of correct answer from the following.

Accepted Answer

When the switch of a circuit is in off position, the circuit will remain open and in this condition, the current does not flow through the circuit.So, option (II) and (III) are correct.

Question 4

Explain the construction and working of electric bell with figure.

Accepted Answer

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Question 5

A rheostat is used in an electrical circuit

Accepted Answer

A rheostat is a variable resistor which is used to control current. they are able to vary the resistance in circuit without interruption. the construction of a rheostat is very similar to potentiometer .Thus A rheostat is used in circuit to change the resistance of the circuit. so option correct is A.

Question 6

What is an electromagnet? Describe the construction and working of an electromagnet with the help of a labelled diagram.

Accepted Answer

An electromagnet is a temporary magnet that works on the magnetic effect of current. It consists of a long coil of insulated copper wire wrapped around a soft iron core that is magnetised only when electric current us passed through the coil. To make an electromagnet, we take a rod $NS$ of soft iron and wind a coil of $C$ of insulated copper wire around it. When the two ends of the copper coil are connected to a battery, an electromagnet is formed.

Question 7

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

Accepted Answer

$\textbf{Explanation}$$\bullet$Potential difference is the difference of electrical potential between two points which is defined as the amount of work energy is required to move an electric charge from one point to another.$\bullet$An electric cell or battery helps to maintain a potential difference across a conductor.$\bullet$The cells only provide the energy required to work on the charge in order to transport it from the negative to the positive terminal. $\bullet$The cell can sustain an electric potential difference across the two ends of the external circuit by giving energy to the charge.

Question 8

Where should we place the key or switch in the electric circuits?

Accepted Answer

The key or Switch can be placed anywhere in the electric circuit.

Question 9

Symbol of electric cell is -

Accepted Answer

(A) This symbol represents bulb(B)This symbol represents electric cell(C)This symbol represents closed switch(D)This symbol represents open switch

Question 10

Read the extract given below and answer the question that follows:The trees inside are moving out into the forest,the forest that was empty all these dayswhere no bird could sitno insect hideno sun bury its feet in shadowthe forest that was empty all these nightswill be full of trees by morning.The figure of speech used in these lines is _________ .(i) Simile (ii) Alliteration(iii) Personification (iv) Metonymy

Accepted Answer

When the push switch is depressed, the circuit is closed. Current passes through the electromagnet winding and the core becomes magnetized. The magnetized core attracts the iron armature which makes the striker hits the gong. However, the movement of the armature opens the make and break switch which switches the electromagnet off. The iron armature springs back to its original position, closing the make and break switch and start the cycle again. Soft iron core is used to make electromagnets as it gains and losses magnetism quickly depending on existence of magnetic fields. The armature is also made of soft iron which can induce magnetism rapidly. No matter what direction is the current flow, the bell rings continuously as long as the push switch is closed because any pole induces the armature.