Chapter 8 : Electricity and Magnetism - Current Electricity - Frank Solutions for Class 9 Physics ICSE

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Chapter 8 - Electricity and Magnetism - Current Electricity Excercise 312

Question 1
What do you mean by an electric current?
Solution 1
The flow of electrons in a particular direction in a conductor is called an electric current.
Question 2
What is an electric cell?
Solution 2
An electric cell is the source of electric current in which chemical energy changes to electrical energy.
Question 3
How much is the charge on an electron?
Solution 3
The charge on an electron is -1.6 x 10-19C.
Question 4
Name the constituents of a cell.
Solution 4
The constituents of cell are two electrodes in the form of conducting rods immersed in the solution called electrolyte.
Question 5
Write SI units of
(i) Electric current,
(ii) Potential difference,
(iii) Resistance.
Solution 5
(i) S. I unit of electric current is Ampere
(ii) S.I unit of potential difference is volt.
(iii) S.I unit of resistance is ohm.
Question 6
What is the number of electrons that would flow per second through the cross-section of a wire when 1 A current flows in it?
Solution 6
I = 1A
T = 1s.
I = Q/t = ne/t
So, n = I . t / e = 1 . (1 / 1.6 x 10-19) = 6.25 x 1018 electrons.
Question 7
0.7 C charges passes through a cross-section of a conductor in 7 s. Find the current.
Solution 7
I = Q/t  = 0.7 / 7 = 0.1 Ampere.
Question 8
Name the instrument used to control current in an electric circuit.
Solution 8
Rheostat is used to control the current in the circuit.

Chapter 8 - Electricity and Magnetism - Current Electricity Excercise 313

Question 1
What is the other name of a variable resistor?
Solution 1
Rheostat is the variable name of electrical resistance.
Question 2
What is the function of a switch in an electric circuit?
Solution 2
Switch is used to put the current on and off in the circuit.
Question 3
Write symbols and state functions of each of the following components in an electric circuit:
(i) Cell
(ii) ammeter
(iii) voltmeter
(iv) key
(v) battery
(vi) rheostat
Solution 3
Question 4
A current of 1.2 A flows through a conductor for 3.0 s. What amount of charge passes through the conductor?
Solution 4
I = Q/ t So, Q = I .t  = 1.2 x 3.0  = 3.6 C.
Question 5
Solution 5
A - is a voltmeter to measure the potential difference, B is an electric resistance to control the current in the circuit , C is the ammeter to measure the magnitude of an electric current, D is cell to provide electric current in circuit, E is an electric key to on and off the circuit, F is the rheostat to control the current in circuit.
Question 6
Solution 6
The slope of the graph represents that with current flowing through a conductor is directly proportional to the potential difference applied the resistance of conductor is constant.
Question 7
What do you mean by the potential difference? Write its SI unit.
Solution 7
Potential difference between two conductors is defined as the amount of work done in moving the unit positive charge from one conductor to another through the wire.
Question 8
Is electric current a scalar quantity?
Solution 8
Yes, electric current is a scalar quantity.
Question 9
State the factors on which the electrical resistance of a wire depends.
Solution 9
The electric resistance of the wire depends on the following factors :
(i)The length of the wire.
(ii)The area of cross-section of the wire.
(iii)The temperature of the wire.
(iv)The material of the wire.
Question 10
What is the SI unit of resistance?
Solution 10
The S.I unit of resistance is ohm.
Question 11
A bulb is connected to a cell. How is the resistance of circuit affected if another identical bulb is connected (i) in series, (ii) in parallel, with the first bulb?
Solution 11
If another bulb is connected in series then the resistance of the wire will increase.
If another bulb is connected in parallel then resistance will decrease.
Question 12
How are the potential difference (V), current (I) and resistance (R) related?
Solution 12
V = I R.
Question 13
'The resistance of a wire is 2 ohm'. Explain the meaning of this statement.
Solution 13
The resistance of the wire is 2 ohms if a current of 1 ampere flows through it when the potential difference across it is 2 volt.
Question 14

Solution 14
The current I = V/R = 14/28 = 0.5 Ampere.
Question 15
State three factors on which the resistance of a wire depends. Explain, how does the resistance depend on the factors stated by you.
Solution 15
The factors on which resistance of the wire depends are :
(i) The length of the wire , resistance is directly proportional to the length of wire.
(ii) The cross-section of the wire , resistance is inversely proportional to the cross-section of the wire.
(iii) The temperature of the wire , resistance of wire is directly proportional to the temperature of the wire.
(iv) The material of the wire (good conductors possess less resistance.)
Question 16
What amount of work is required in moving 3 C charge through a potential difference of 6 V?
Solution 16
W = V.Q = 6. 3 = 18Joule.
Question 17
What is the physical meaning of resistance?
Solution 17
The resistance of the conductor is the property due to which it opposes the flow of current in it.
Question 18
'The potential difference between two conductors is 1 volt'. Explain, the meaning of this statement.
Solution 18
The potential difference between two points is 1 volt if the work done in transferring 1 coulomb of charge from one point to another point is 1 joule.