Electricity For Class 10 Physics Important Questions and Answers
Q 1 –The substances which have a large number of free electrons and offer a low resistance are called
(a) insulators
(b) inductors
(c) semi-conductors
(d) conductors
Ans. (d) conductors
Q 2 – Out of the following which is an insulating material ?
(a) Copper
(b) Gold
(c) Silver
(d) Paper
Ans. (d) conductors
Q 3 – The resistance of a conductor varies inversely as
(a) length
(b) area of cross-section
(c) temperature
(d) resistivity
Ans. (b) area of cross-section
Q 4 – With rise in temperature the resistance of pure metals
(a) increases
(b) decreases
(c) first increases and then decreases
(d) remains constant
Ans. (b) area of cross-section
Q 5 – The resistance of a parallel circuit consisting of two branches is 12 ohms. If the resistance of one branch is 18 ohms, what is the resistance of the other ?
(a) 18
(b) 36
(c) 48
(d) 64
Ans. (b) 36
Q 6 – A current of 16 amperes divides between two branches in parallel of resistances 8 ohms and 12 ohms respectively. The current in each branch is
(a) 6.4 A, 6.9 A
(b) 6.4 A, 9.6 A
(c) 4.6 A, 6.9 A
(d) 4.6 A, 9.6 A
Ans. (b) 6.4 A, 9.6 A
Q 7 – You have to replace 1500 resistor in radio. You have no 1500 resistor but have several 1000 ones which you would connect
(a) two in parallel
(b) two in parallel and one in series
(c) three in parallel
(d) three in series
Ans. (b) two in parallel and one in series
Q 8 – Which of the following statement is true both for a series and a parallel D.C. circuit?
(a) Elements have individual currents
(b) Currents are additive
(c) Voltages are additive
(d) Power are additive
Ans. (d) Power are additive
Q 9 – How voltmeter should be connected to a resistor in order to find potential difference across it.?
Ans. It is connected parellel to resistor.
Q 10 – Why are coils of electric toasters and electric irons made of alloy rather than pure metals?
Ans. Alloys are preferred to make coils of toasters and irons because they have higher resistivity and do not oxidize easily at high temperature.
Q 11 – Write S.I. unit of resistivity.
Ans. Ohm-metre (Ωm).
Q 12 – 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’.
Ans.– Heat produced, H = VIt
Q 13 – An ammeter is always connected in series across a circuit element. What happens when it is connected in parallel with a circuit element?
Ans. An ammeter is a low-resistance device. When it is connected in parallel, the resistance of the circuit reduces considerably. Therefore, a large current flows through the circuit, by virtue of circuit element may damage.
Q 14 – 320 J of heat is produced in 10s in a 2Ω resistor. Find amount of current flowing through the resistor?
Ans. Given,
Heat produced H=320J
Time taken t=10s
Resistance of resistor R=2Ω
Current I (let)
Since, H=I2Rt
I2= H/Rt = 320J/(2×10s) = 16(A)2
I=4A
So, 4A of current is flowing through the resistor.
Q 15 – Derive an expression for electric energy consumed in a device in terms of I, t, and R where I is the current drawn by the resistor R and t is the time for which the current flows?
Ans. We know that work done = W = QV
V is potential difference, Q is charge passed.
V=IR
Now, we know current I=Q/t
Q=It
In t times Q charge has been passed.
W=It IR
W=I2tR
So, electric energy consumed is given as
W=I2Rt
Q 16 – State the different ways, three resistors each having resistance r can be connected so that they will draw maximum current from the circuit. Explain?
Ans. The three resistors will draw maximum current when are equivalent resistance will be minimum. This is the case when the resistors are connected in parallel with each other. In this case, the equivalent resistance will be R
Then,
1/R=1/r+1/r+1/r
1/R=3/r
R=r/3
In this case, maximum current will be drawn from the battery.
The minimum current will be drawn from the circuit, when resistance is maximum.
This is the case, when resistances are connected in series.
The equivalent resistance of the system will be
R’=r+r+r=3r
In this case, minimum current will be drawn from the battery.
Q 17 – (a) Calculate the resistance of 1 km long copper wire of radius 1 mm. The resistivity of the copper is 1.72 x 10 Ω m.
(b) Draw a schematic diagram of a circuit consisting of a battery of 4 cells of 2V each connected to a key, an ammeter and two resistors of 2 Ω and 3 Ω respectively in series and a voltmeter to measure potential difference across 3.
Ans.
Q 18 – Three bulbs each having power P are connected in series in an electric circuit.
In another circuit, another set of three bulbs of same power are connected in parallel to the same source.
(i) Will the bulbs in both the circuits glow with the same brightness? Justify your answer.
(ii) Now let one bulb in each circuit get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.
(iii) Representing each bulb by a resistor, draw circuit diagram for each case.
Ans. (i) Bulbs in parallel provide more illumination. This is because
(a) each bulb gets same voltage and is equal to the applied voltage.
(b) each bulb draws required current from the mains. Hence, they work properly.
(ii)When one bulb in each circuit get fused, In series: Rest of the bulbs will not glow. This is because in series arrangement, there is only a single path for the flow of current.
In parallel: Rest of the bulbs will continue to glow as in parallel connection,
(a) individual branch in the circuit completes its own circuit, or
(b) different paths are available for the flow of current.
(iii)
For Parallel
For Series
Q 19 – Two devices of rating 44 W, 220 V and 11 W, 220 V are connected in series. The combination is connected across a 440 V mains. The fuse of which of the two
devices is likely to burn when the switch is ON? Justify your answer.
