Question 1

Question 4Write symbols and state functions of each of the following components in an electric circuit —(i) key(ii) cell(iii) rheostat(iv) ammeter(v) voltmeter

Accepted Answer

The symbol and function of the components are as follows —(i) KeySymbol:Function:A key is used to put the current on and off in a circuit.(ii) CellSymbol:Function:A cell acts as a source of direct current for the circuit.(iii) RheostatSymbol:Function:It controls the flow of current in a circuit.(iv) AmmeterSymbol:Function:An ammeter is an instrument used to measures the magnitude of current flowing in a circuit.(v) VoltmeterSymbol:Function:A voltmeter is used to measure the potential difference between two points of a circuit.

Question 2

Question 5In the electric circuit shown in the figure below, label the parts A, B, C, D, E, and F. State the function of each part. Show in the diagram the direction of flow of current.

Accepted Answer

The diagram below shows the direction of flow of current marked by red arrows and the labelled parts — A, B, C, D, E, and FThe name and function of each part is as follows —A → Ammeter.An ammeter is an instrument used to measure the magnitude of current flowing in a circuit.B → Cell.It acts as a source of direct current for the circuit.C → key.It is used to put the current on and off in the circuit.D → Load.An appliance which is connected in a circuit. It may be a resistance (e.g., bulb, heater etc.) or a combination of different electrical components.E → Voltmeter.A voltmeter is used to measure the potential difference between two points of a circuit.F → Rheostat.A rheostat is a device by which resistance in a circuit can be varied continuously.

Question 3

Question 6(a) Complete the circuit given in figure by inserting between the terminals A and C, an ammeter. (b) In the diagram mark the polarity at the terminals of ammeter and indicate clearly the direction of flow of current in the circuit, when the circuit is complete. (c) Name and state the purpose of Rh in the circuit.

Accepted Answer

(a) The circuit with ammeter between the terminals A and C with polarity marked is shown below:(b) The direction of flow of current in the completed circuit with ammeter (polarity marked) is shown below:(c) Rh is the rheostat. It controls the flow of current in a circuit.

Question 4

Question 8A battery is correctly represented by :

Accepted Answer

Reason — A battery is formed by joining a number of cells together in series (i.e., cathode of one cell connected to the anode of another cell).

Question 5

Question 12A ............... is either used to detect the presence of a weak current or to only know the direction of flow of current in a circuit.ammetergalvanometervoltmeterrheostat

Accepted Answer

galvanometerReason — A galvanometer is used to either detect the presence of a weak current or to only know the direction of flow of current in a circuit. It does not measure the magnitude of current in a circuit.

Question 6

Question 13Insulators have	............... electrons and conductors have ............... electrons.no free, large number of freelarge number of free, no freeno free, small number of freesmall number of free, no free

Accepted Answer

no free, large number of freeReason — Insulators have no free electrons and offer very high resistance and conductors have large number of free electrons and they offer very small resistance to the flow of electrons.

Question 7

Question 14An insulator of electricity is:copperacidulated waterhuman bodysilk

Accepted Answer

silkReason — Silk does not conduct electricity, hence is an insulator.

Question 8

Question 15The presence of ...............	in the path makes a circuit incomplete and current does not flow.conductorammetervoltmeterinsulator

Accepted Answer

insulatorReason — The presence of insulator in the path makes a circuit incomplete and current does not flow.

Question 9

Question 16Select the insulator among the followingPure waterHuman bodyAluminiumMercury

Accepted Answer

Pure waterReason — Pure water is a good insulator as it has a low concentration of ions so it does not conduct electricity very well. On the other hand, the human body, aluminum, and mercury are not good insulators. The human body contains electrolytes and can conduct electricity. Aluminum is a metal and is highly conductive. Mercury is a liquid metal and also conducts electricity well.

Question 10

Question 17Connecting wires are made of substances that have :highly conducting materialnegligible resistancefree electrons in a large numberall of these

Accepted Answer

all of theseReason — Connecting wires are typically made of substances, such as copper or aluminum, that possess highly conducting materials, negligible resistance, and a large number of free electrons. These characteristics allow for efficient flow of electric current through the wires.

Question 11

Question 18Out of the following circuits shown, the bulb glows in which one?

Accepted Answer

option 4Reason — In circuit 4, the key is closed, completing the circuit. In the other circuits the key (K) is left open, so the circuits are incomplete. For an electric circuit to function, every component must conduct current. If the circuit is broken at any point, the circuit remains open and no current flows.

Question 12

Question 3When starter motor of a car is switched on for 0.8 s, a charge 24 C passes through the coil of the motor. Calculate the current in the coil.

Accepted Answer

Given,Time = 0.8 scharge = 24 Ccurrent = ?I=Qt\text I = \dfrac{\text Q}{\text t}I=tQ​Substituting the values we get,I=240.8⇒I=30 A\text I = \dfrac{24}{0.8} \[0.5em] \Rightarrow \text I = 30 \text { A}I=0.824​⇒I=30 AHence, the current in the coil = 30 A

Question 13

Question 9A galvanometer has an 'O' mark at the middle, while a voltmeter and ammeter has the mark at the left hand corner of the dial. Explain.

Accepted Answer

A galvanometer is used to know the direction of flow of current in a circuit. Current can enter or leave through any of its terminals, therefore it has just an 'O' mark at the middle and no +/- signs at its terminals.On the other hand, Ammeter and Voltmeter measure the current and voltage in the circuit, respectively. Therefore, the + sign marked at the left hand corner indicates that current must enter through this terminal.

Question 14

Question 10The resistance of a conductor would be ............... if a current of 2 A flows through it when the potential difference across its ends is 2 volt.2Ω0Ω1Ω4Ω

Accepted Answer

1ΩReason — As, R = VI\dfrac{	ext{V}}{	ext{I}}IV​I = 2AV = 2 voltHence, R = 22\dfrac{2}{2}22​ = 1Ω

Question 15

Question 11While performing an experiment, a student reduces the resistance to one half keeping the potential difference same. New reading of the current will be :halfdoublefour timesone fourth

Accepted Answer

doubleReason — Let initial and final current be I and Inew, initial and final resistance is R and Rnew and initial and final potential be V and VnewFrom Ohm's law,Case 1 :V=IR\text V = \text {IR}V=IRCase 2 :Vnew=InewRnew\text V_{\text {new}} = \text I_{\text {new}}\text R_{\text {new}}Vnew=InewRnewAccording to question,Vnew=V and Rnew=12R⇒InewRnew=IR⇒Inew×12R=IR⇒Inew2=I⇒Inew=2I\text V_{\text {new}}=\text V\ \text { and}\ \text { R}{\text {new}}=\dfrac {1}{2}\text R\[1 em] \Rightarrow \text I{\text {new}}\text R_{\text {new}} = \text {IR} \[1 em] \Rightarrow \text I_{\text {new}}\times \dfrac{1}{2}\text R = \text {IR} \[1 em] \Rightarrow \dfrac{\text I_{\text {new}}}{2} = \text I \[1 em] \Rightarrow \text I_{\text {new}} = 2\text IVnew=V and Rnew=21R⇒InewRnew=IR⇒Inew×21R=IR⇒2Inew=I⇒Inew=2I

Question 16

Question 1In transferring 1.5 C charge through a wire, 9 J of work is done. Find the potential difference across the wire.

Accepted Answer

Given,charge (q) = 1.5 Cwork = 9 Jpotential difference across the wireV=Wq\text V = \dfrac{\text W}{\text q}V=qW​Substituting the values in the formula, we get,V=91.5⇒V=6 V\text V = \dfrac{9}{1.5} \[0.5em] \Rightarrow \text V = 6\ \text VV=1.59​⇒V=6 VHence, the potential difference across the wire = 6 V.

Question 17

Question 2How is the current flowing in a conductor changed if the resistance of conductor is doubled keeping the potential difference across it the same?

Accepted Answer

According to Ohm's law,V=IR⇒I=VR\text{V} = \text{I}\text{R} \[0.5em] \Rightarrow \text{I} = \dfrac{\text V}{\text R} \[1em]V=IR⇒I=RVLet the doubled resistance be 2R. Potential difference remains the sameInew=V2R⇒Inew=I2\text{I}{\text{new}} = \dfrac{\text V}{2\text R} \[0.5em] \Rightarrow \text{I}{\text{new}} = \dfrac{\text I}{2}Inew=2RV⇒Inew=2I∴ If the resistance of conductor is doubled keeping the potential difference across it the same then current flowing in a conductor will be halved.

Question 18

Question 7Define the term potential difference.

Accepted Answer

Potential difference between two conductors is equal to the work done in transferring a unit positive charge from one conductor to the other conductor.If work W is done in transferring a test charge q from one conductor to the other, the potential difference between them isV1−V2=Wq	ext V_1 - 	ext V_2 = \dfrac{	ext W}{	ext q}V1​−V2​=qW​Potential difference is a scalar quantity.

Current Electricity

Exercise 9A Long Answer Type

Exercise 9A Multiple Choice Type

Exercise 9A Numericals

Exercise 9A Short Answer Type

Exercise 9B Multiple Choice Type

Exercise 9B Numericals

Exercise 9B Short Answer Type

Exercise 9B Very Short Answer Type