Objective Physics for NEET

Abhay Kumar

Chapter 19

Heating and Chemical Effect of Current - all with Video Answers

Educators

Chapter Questions

Problem 1

The electric current passing through a metallic wire produces heating because of
(a) collisions of conduction electrons with each other
(b) collisions of the atoms of the metal with each other
(c) the energy released in the ionisation of the atoms of the metal
(d) collisions of the conduction electrons with the atoms of the metallic wire

Satpal Satpal

Satpal Satpal

Numerade Educator

Problem 2

The material of the fuse wire should have
(a) a high specific resistance and a high melting point
(b) a low specific resistance and a low melting point
(c) a high specific resistance and a low melting point
(d) a low specific resistance and a high melting point

Satpal Satpal

Numerade Educator

Problem 3

Cause of heat production in a current carrying conductor is
(a) collisions of free electrons with one another
(b) high drift speed of free electrons
(c) collisions of free electrons with atoms or ions of the conductor
(d) high resistance value

Satpal Satpal

Numerade Educator

Problem 4

The thermocouple is based on the principle of
(a) Seebeck effect
(b) Thomson effect
(c) Peltier effect
(d) Joule effect

Satpal Satpal

Numerade Educator

Problem 5

When a current passes through the junction of two different metals, evolution or absorption of heat at the junction is known as
(a) Joule effect
(b) Seebeck effect
(c) Peltier effect
(d) Thomson effect

Satpal Satpal

Numerade Educator

Problem 6

As the temperature of hot junction in a thermocouple increases, thermo electromotive force
(a) always increases with temperature
(b) is always positive
(c) first increases with temperature and then decreases with temperature but never becomes negative
(d) can be positive as well as negative

Satpal Satpal

Numerade Educator

Problem 7

The thermoelectric current, at the temperature of inversion
(a) flows from copper to iron through hot junction
(b) flows from iron to copper through hot junction
(c) is maximum
(d) does not depend on the temperature of the cold junction

Satpal Satpal

Numerade Educator

Problem 8

When a current passes through a wire whose different parts are maintained at different temperatures, evolution or absorption of heat all along the length of wire is know as
(a) Joule effect
(b) Seebeck effect
(c) Peltier effect
(d) Thomson effect

Satpal Satpal

Numerade Educator

Problem 9

Which one of the following statements is wrong?
(a) Seebeck effect is irreversible
(b) Peltier effect is localized at the junction
(c) Joule heating effect is independent of the direction of the flow of the current in a conductor
(d) Thomson effect is similar in origin to that of Peltier effect. They are both due to non-uniform distribution of electrons in metals

Satpal Satpal

Numerade Educator

Problem 10

In Seebeck effect, Sb appears before Bi; therefore in Sb-Bi thermocouple current flows from:
(a) Sb to Bi through hot junction
(b) Sb to Bi through cold junction
(c) Bi to Sb through cold junction
(d) none of the above

Satpal Satpal

Numerade Educator

Problem 11

The value of Peltier coefficient of a thermocouple:
(a) does not vary with absolute temperature of the junction
(b) varies with absolute temperature of the junction
(c) does not depend on the two different metals forming the junction
(d) varies with the direction of current

Satpal Satpal

Numerade Educator

Problem 12

First order derivation of thermo emf produced in thermo-couple with respect to temperature gives:
(a) inversion temperature
(b) thomson coefficient
(c) neutral temperature
(d) thermoelectric power

Satpal Satpal

Numerade Educator

Problem 13

Antimony and bismuth are usually used in a thermocouple because:
(a) negative thermo emf is produced
(b) constant thermo emf is produced
(c) lower thermal emf is produced
(d) higher thermal emf is produced

Satpal Satpal

Numerade Educator

Problem 14

The thermocouple among the following that can produce maximum thermo emf for the same temperature difference between the junction is:
(a) $\mathrm{Fe}-\mathrm{Cu}$
(b) $\mathrm{Ag}-\mathrm{Au}$
(c) $\mathrm{Sb}-\mathrm{Bi}$
(d) $\mathrm{Cu}-\mathrm{Pb}$

Satpal Satpal

Numerade Educator

Problem 15

Which of the following describes the ratio between thermo electric coefficient $\alpha$ and $\beta$ ?
(a) Temperature of inversion
(b) Thermo electric power
(c) Neutral temperature
(d) Qualitative temperature of inversion

Satpal Satpal

Numerade Educator

Problem 16

The charge flowing through a resistance $R$ varies with time according to $Q=a t-b t^{2} .$ The total heat produced in $R$ is:
(a) $\frac{a^{3} R}{6 b}$
(b) $\frac{a^{3} R}{2 b}$
(c) $\frac{a^{3} R}{3 b}$
(d) $\frac{a^{3} R}{b}$

Satpal Satpal

Numerade Educator

Problem 17

A constant voltage is applied between the two ends of a uniform metallic wire. Some heat is developed in it. The heat developed is doubled if:
(a) both the length and radius of the wire are halved
(b) both the length and radius of the wire are doubled
(c) the radius of the wire is doubled
(d) the length of the wire is doubled

Satpal Satpal

Numerade Educator

Problem 18

A resistor $R_{1}$ dissipates the power $P$ when connected to a certain generator. If a resistor $R_{2}$ is put in series with $R_{1}$, the power dissipated by $R_{1}$ :
(a) decreases
(b) increases
(c) remains the same
(d) any of the above depending upon the relative values of $R_{1}$ and $R_{2}$

Satpal Satpal

Numerade Educator

Problem 19

You are given resistance wire of length $50 \mathrm{~cm}$ and a battery of negligible resistance. In which of the following cases is the largest amount of heat generated?
(a) When the wire is connected to the battery directly.
(b) When the wire is divided into two parts and both the parts are connected to the battery in parallel.
(c) When the wire is divided into four parts and all the four parts are connected to battery in parallel.
(d) When only half of the wire is connected to the battery.

Satpal Satpal

Numerade Educator

Problem 20

When a current is divided between two resistors according to Kirchhoff's law, then the heat produced is:
(a) zero
(b) negligible
(c) minimum
(d) maximum

Satpal Satpal

Numerade Educator

Problem 21

Two heating coils one of fine wire and the other of thick wire made of the same material and of the same length are connected in series and in parallel. Which of the following statements is correct?
(a) In series fine wire will liberate more energy while in parallel thick one will liberate more energy.
(b) In series fine wire will liberate less energy while in parallel more energy.
(c) Both will liberate equal energy.
(d) In series thick wire will liberate more energy, while in parallel less energy.

Satpal Satpal

Numerade Educator

Problem 22

Fifty electric bulbs are connected in series across the mains of a 220 volts supply. After one bulb is fused, the remaining 49 bulbs are again connected in series across the same mains. The illumination will be:
(a) more with 50 bulbs than with 49 bulbs
(b) more with 49 bulbs than with 50 bulbs
(c) equal in both cases
(d) in the ratio $50^{2}: 49^{2}$ in the first and second case respectively

Satpal Satpal

Numerade Educator

Problem 23

A heater of 220 volt boils a volume of water in $5 \mathrm{~min}-$ utes time. If the heater is operated at 110 volt the same volume of water will boil in:
(a) 5 minute
(b) 8 minute
(c) 10 minute
(d) 20 minute

Satpal Satpal

Numerade Educator

Problem 24

A heating coil is labelled $100 \mathrm{~W}-220 \mathrm{~V}$. The coil is cut into two equal halves and the two pieces are joined in parallel to the same source. The energy now liberated per sec is:
(a) $200 \mathrm{~J}$
(b) $400 \mathrm{~J}$
(c) $25 \mathrm{~J}$
(d) $50 \mathrm{~J}$

Satpal Satpal

Numerade Educator

Problem 25

A 25 watt- 220 volt bulb and a 100 watt- 220 volt bulb are connected in series across a 220 volt line; which electric bulb will glow more brightly?
(a) 25 watt bulb
(b) 100 watt bulb
(c) Both will have equal incandescence
(d) Neither will give light

Satpal Satpal

Numerade Educator

Problem 26

An electric heater has resistance $150 \mathrm{ohm}$ and can bear a maximum current of 1 ampere. if the heater is to be used on 220 volt mains, the least resistance required in the circuit will be:
(a) $70 \mathrm{ohm}$
(b) $50 \mathrm{ohm}$
(c) $2.5 \mathrm{ohm}$
(d) $1.4 \mathrm{ohm}$

Satpal Satpal

Numerade Educator

Problem 27

By how many per cent will the power in a lamp decrease if the current drops by 1 per cent?
(a) $0.1$ per cent
(b) 1 per cent
(c) 2 per cent
(d) 4 per cent

Satpal Satpal

Numerade Educator

Problem 28

Two electric bulbs have tungsten filaments of same length. If one of them gives 60 watts and the other 100 watts, then:
(a) 100 watt bulb has thicker filament
(b) 60 watt bulb has thicker filament
(c) both filaments are of same thickness
(d) it is impossible to get different wattage unless the lengths are different

Satpal Satpal

Numerade Educator

Problem 29

Resistances of one carbon filament and one tungsten lamp are measured individually when the lamps are lit and compared with their respective resistances when cold. Which one of the following statements will be true?
(a) Resistance of the carbon filament lamp will increase but that of tungsten will diminish when hot.
(b) Resistance of the tungsten filament lamp will increase but that of carbon will diminish when hot.
(c) Resistances of both the lamps will increase when hot.
(d) Resistances of both the lamps will decrease when hot.

Satpal Satpal

Numerade Educator

Problem 30

An electric kettle has two coils; when one of these is switched on the water in the kettle boils in 6 minute. When the other coil is switched on, the water boils in 3 minute. if the two coils are connected in series, the time taken to boil the water in the kettle is:
(a) 3 minute
(b) 6 minute
(c) 2 minute
(d) 9 minute

Satpal Satpal

Numerade Educator

Problem 31

Two resistance thermometers are made, one of platinum wire and the other of germanium. The resistances of both the thermometers are equal at room temperature. the two resistance wires are connected in series and the two resistance wires are heated to $100^{\circ} \mathrm{C}$. The potential drop in the two resistances is measured. Which of the following statements is correct?
(a) The potential drop across the platinum wire is equal to the potential drop across the germanium wire.
(b) The potential drop across the platinum wire is greater than that across germanium wire.
(c) The potential drop across the platinum wire is less than that across germanium wire.
(d) The nature of the potential drop canto be ascertained unless the magnitude of current is given.

Saman Zulfiqar

Numerade Educator

Problem 32

If a wire of resistance $20 \Omega$ is covered with ice and a voltage of $210 \mathrm{~V}$ is applied across the wire, then the rate of melting of ice is:
(a) $8.85 \mathrm{~g} / \mathrm{sec}$
(b) $1.92 \mathrm{~g} / \mathrm{sec}$
(c) $6.56 \mathrm{~g} / \mathrm{sec}$
(d) none of these

Satpal Satpal

Numerade Educator

Problem 33

A factory is served by a 220 volt supply line. In a circuit protected by a fuse marked 10 ampere, the maximum number of 100 watt lamps in parallel that can be turned on is:
(a) 11
(b) 22
(c) 33
(d) 66

Satpal Satpal

Numerade Educator

Problem 34

If $t_{1}$ and $t_{2}$ are the time taken by two different coils for producing same heat with same supply, then the time taken by them to produce the same heat when connected in parallel will be:
(a) $\frac{t_{1} t_{2}}{t_{1}+t_{2}}$
(b) $t_{1}+t_{2}$
(c) $t_{1} t_{2}$
(d) $\frac{t_{1}+t_{2}}{t_{1} t_{2}}$

Satpal Satpal

Numerade Educator

Problem 35

It takes 16 minute to boil some water in an electric kettle. Due to some defect is becomes necessary to remove $10 \%$ turns of heating coil of the kettle. After repairs, how much time will it take to boil the same mass of water?
(a) $17.7$ minute
(b) $14.4$ minute
(c) $20.9$ minute
(d) $13.7$ minute

Satpal Satpal

Numerade Educator

Problem 36

Figure shows three similar lamps $L_{1}, L_{2}$ and $L_{3}$ connected across a power supply. If the lamp $L_{3}$ fuses, how will the light emitted by $L_{1}$ and $L_{2}$ change?
(a) No change
(b) Brilliance of $L_{1}$ decreases and that of $L_{2}$ increases
(c) Brilliance of both $L_{1}$ and $L_{2}$ increases
(d) Brilliance of both $L_{1}$ and $L_{2}$ decreases

Satpal Satpal

Numerade Educator

Problem 37

The resistance of a carbon filament at $0^{\circ} \mathrm{C}$ is $104 \Omega .$ It is connected in series to an iron wire. The temperature coefficients of resistivity of carbon and iron are $-$ $0.0003 /{ }^{\circ} \mathrm{C}$ and $0.0052 /{ }^{\circ} \mathrm{C}$ respectively. What must be the resistance of the iron wire so that the combined resistance does not change with temperature?
(a) $6 \Omega$
(b) $15 \Omega$
(c) $(156 / 104) \Omega$
(d) $(3 / 52) \Omega$

Satpal Satpal

Numerade Educator

Problem 38

An electrical cable having a resistance of $0.2 \Omega$ delivers $10 \mathrm{~kW}$ at $200 \mathrm{~V} \mathrm{DC}$ to a factory. What is the efficiency of transmission?
(a) $65 \%$
(b) $75 \%$
(c) $85 \%$
(d) $95 \%$

Satpal Satpal

Numerade Educator

Problem 39

Three equal resistances each of $10 \Omega$ are connected as shown in figure. The maximum power consumed by each resistor is $20 \mathrm{~W}$. The maximum power consumed by the combination is:
(a) $60 \mathrm{~W}$
(b) $30 \mathrm{~W}$
(c) $15 \mathrm{~W}$
(d) none of these

Satpal Satpal

Numerade Educator

Problem 40

A condenser of capacity $5 \mu \mathrm{F}$ is connected to a constant source of emf 200 volt as shown in figure. What will be the amount of heat produced in $R_{1}$ when the key is thrown from contact 1 to $2 ?$
(a) $0.6 \mathrm{~J}$
(b) $0.06 \mathrm{~J}$
(c) $6 \mathrm{~J}$
(d) $20 \mathrm{~J}$

Satpal Satpal

Numerade Educator

Problem 41

By means of an electric immersion heater connected to 240 volt mains, it is required to heat 100 litres of water from $20^{\circ} \mathrm{C}$ to $70^{\circ} \mathrm{C}$ in 2 hours. Assuming no heat loss. the current necessary to effect this is
(a) $20.2 \mathrm{amp}$
(b) $12.1 \mathrm{amp}$
(c) $6 \mathrm{amp}$
(d) $18.1 \mathrm{amp}$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 42

Two electric bulbs rated $P_{1}$ watt- $V$ volt and $P_{2}$ watt-V volt are connected in parallel and $V$ volt are applied to it. The total power will be
(a) $\frac{P_{1} P_{2}}{P_{1}+P_{2}}$ watt
(b) $\sqrt{P_{1} P_{2}}$ watt
(c) $\left(P_{1}+P_{2}\right)$ watt
(d) $\frac{P_{1}+P_{2}}{P_{1} P_{2}}$ watt

Satpal Satpal

Numerade Educator

Problem 43

Consider the four circuits shown in the figure given below. In which circuit the power dissipated is the greatest? (Neglect the internal resistance of the power supply)
(a)
(b)
(c) $\xi \frac{\sqrt{2}}{L} R \frac{\xi \xi}{\xi} R$
(d) $\left.\xi \frac{\Gamma}{R^{\frac{1}{\xi}}}\right\} R$

Satpal Satpal

Numerade Educator

Problem 44

In the previous question left end of the conductor is maintained at zero potential and right end at $+V_{0}$. If at a distance $x$ from left end, potential is equal to $V$, which of the following graphs is correct?

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 45

If $E$ denotes electric field in a uniform conductor and $v_{d}$ the corresponding drift velocity of free electrons in the conductor then which of the following graphs is correct?

Saman Zulfiqar

Numerade Educator

Problem 46

If the cold junction is held at $0^{\circ} \mathrm{C}$, the thermo $\mathrm{emf} V$ of a thermocouple varies as $V=10 \times 10^{-6} t-\frac{1}{40} \times$ $10 \times 10^{-6} t^{2}$, where $t$ is the temperature of the hot junction in ${ }^{\circ} \mathrm{C}$. The neutral temperature and the maximum value of thermo emf are respectively
(a) $200^{\circ} \mathrm{C} ; 2 \mathrm{mV}$
(b) $400^{\circ} \mathrm{C} ; 2 \mathrm{mV}$
(c) $100^{\circ} \mathrm{C} ; 1 \mathrm{mV}$
(d) $200^{\circ} \mathrm{C} ; 1 \mathrm{mV}$

Satpal Satpal

Numerade Educator

Problem 47

In a thermocouple, the temperature of the cold junction and the neutral temperature are $-40^{\circ} \mathrm{C}$ and $275^{\circ} \mathrm{C}$ respectively. If the cold junction temperature is increased by $60^{\circ} \mathrm{C}$, the neutral temperature and temperature of inversion respectively becomes
(a) $275^{\circ} \mathrm{C}, 530^{\circ} \mathrm{C}$
(b) $355^{\circ} \mathrm{C}, 530^{\circ} \mathrm{C}$
(c) $275^{\circ} \mathrm{C}, 590^{\circ} \mathrm{C}$
(d) $355^{\circ}, 590^{\circ} \mathrm{C}$

Satpal Satpal

Numerade Educator

Problem 48

If the cold junction of a thermocouple is kept at $0^{\circ} \mathrm{C}$ and the hot junction is kept at $T^{\circ} \mathrm{C}$, then the relation between neutral temperature $\left(T_{n}\right)$ and temperature of inversion $(T)$ is
(a) $T=T$
(b) $T_{n}=T / 2$
(c) $T_{n}=2 T_{i}$
(d) $T_{i}=\alpha T_{n}+\beta T_{n}^{2}$

Satpal Satpal

Numerade Educator

Problem 49

The thermo emf $\xi$ in volts of a certain thermocouple is found to vary with temperature $T$ of hot junction while cold junction is kept at $0^{\circ} \mathrm{C}$, as
$$
\xi=40 T-\left(T^{2} / 20\right)
$$
The neutral temperature of the couple is:
(a) $100^{\circ} \mathrm{C}$
(b) $200^{\circ} \mathrm{C}$
(c) $400^{\circ} \mathrm{C}$
(d) $800^{\circ} \mathrm{C}$

Satpal Satpal

Numerade Educator

Problem 50

The emf developed in a thermocouple is given by
$$
\xi=\alpha T+\frac{1}{2} \beta T^{2}
$$
where $\mathrm{T}$ is the temperature of hot junction, the cold junction being at $0^{\circ} \mathrm{C}$. The thermoelectric power of the couple is
(a) $\alpha+\frac{\beta}{2} T$
(b) $\alpha+\beta T$
(c) $\frac{\alpha T^{2}}{2}+\frac{\beta T^{3}}{6}$
(d) $\frac{\alpha}{2 \beta}$

Satpal Satpal

Numerade Educator

Problem 51

The emf generated across a thermocouple, with cold junction at $0^{\circ} \mathrm{C}$ is $\xi=a \theta+b \theta^{2}$, with $a=30 \mu \mathrm{V}\left({ }^{\circ} \mathrm{C}\right)^{-1}$
and $b=0.08 \mu \mathrm{V}\left({ }^{\circ} \mathrm{C}\right)^{-2}$. As $\xi=6 \mu \mathrm{V}$, the hot junction
temperature is about
(a) $14^{\circ} \mathrm{C}$
(b) $144^{\circ} \mathrm{C}$
(c) $323^{\circ} \mathrm{C}$
(d) $519^{\circ} \mathrm{C}$

Saman Zulfiqar

Numerade Educator

Problem 52

The thermo emf produced in a thermocouple is 3 microvolts per degree centigrade. if the temperature of the cold junction is $20^{\circ} \mathrm{C}$ and the thermo $\mathrm{emf}$ is $0.3 \mathrm{mil}-$ livolts, the temperature of the hot junction is
(a) $80^{\circ} \mathrm{C}$
(b) $100^{\circ} \mathrm{C}$
(c) $120^{\circ} \mathrm{C}$
(d) $140^{\circ} \mathrm{C}$

Satpal Satpal

Numerade Educator

Problem 53

Which arrangement of four identical resistances should be used to draw maximum energy from a cells of voltage $V ?$
(a)
(b)
(c)
(d)

Saman Zulfiqar

Numerade Educator

Problem 54

A cylindrical conductor has uniform cross-section. Resistivity of its material increases linearly from left end to right end. If a constant current is flow ing through it and at a section of distance $x$ from left end, magnitude of electric field intensity is $E$. Which of the following graphs is correct?
(a)
(b)
(c)
(d)

Satpal Satpal

Numerade Educator

Problem 55

The speed of rotation of a fan is reduced by putting a rheostat in series with the fan. in this case we can assume
(a) less power than that at full speed but more efficiency
(b) less power than that at full speed but less efficiency
(c) the same power as at full speed
(d) more power than at full speed

Satpal Satpal

Numerade Educator

Problem 56

Thermocouple is an arrangement of two different metals
(a) to convert heat energy into electrical energy
(b) to produce more heat
(c) to convert heat energy into chemical energy
(d) to convert electrical energy into heat energy

Satpal Satpal

Numerade Educator

Problem 57

Bulb $B_{1}(100 \mathrm{~W}-250 \mathrm{~V})$ and bulb $B_{2}(100 \mathrm{~W}-200$
V) are connected across $250 \mathrm{~V}$. What is potential drop $\operatorname{across} B_{2} ?$
(a) $200 \mathrm{~V}$
(b) $250 \mathrm{~V}$
(c) $98 \mathrm{~V}$
(d) $48 \mathrm{~V}$

Satpal Satpal

Numerade Educator

Problem 58

One junction of a certain thermoelectric couple is at a fixed temperature $T_{r}$ and the other junction is at temperature $T$. The thermo-electromotive force for this is expressed by: $\xi=k(T-T)\left[T_{o}-\frac{1}{2}\left(T+T_{r}\right)\right] .$ At temperature $T=\frac{1}{2} T_{o}$, the thermoelectric power is
(a) $\frac{1}{2} k T_{o}$
(b) $k T_{o}$
(c) $\frac{1}{2} k T_{0}^{2}$
(d) $\frac{1}{2} k\left(T_{o}-T_{r}\right)^{2}$

Satpal Satpal

Numerade Educator

Problem 59

The ratio of cross-sectional areas of two conducting wires made up of same material and having same length is 1: $2 .$ What will be the ratio of heat produced per second in the wires, when same current is flowing in them?
(a) $1: 4$
(b) $2: 1$
(c) $1: \sqrt{2}$
(d) $1: 1$

Satpal Satpal

Numerade Educator

Problem 60

Three electric bulbs of $200 \mathrm{~W}, 200 \mathrm{~W}$ and $400 \mathrm{~W}$ are shown in figure. The resultant power of the combination is:
(a) $800 \mathrm{~W}$
(b) $400 \mathrm{~W}$
(c) $200 \mathrm{~W}$
(d) $600 \mathrm{~W}$

Satpal Satpal

Numerade Educator

Problem 61

Two electric bulbs one of $200 \mathrm{~V}-40 \mathrm{~W}$ and other of 200 V-100 W are connected in series to a 200 volt line, then:
(a) the potential drop across two bulbs is same
(b) the potential drop across $40 \mathrm{~W}$ bulb is greater than the potential drop across $100 \mathrm{~W}$ bulb
(c) the potential drop across $100 \mathrm{~W}$ bulb is greater than potential drop across $40 \mathrm{~W}$ bulb
(d) the potential drop across both the bulbs is 200 volt

Saman Zulfiqar

Numerade Educator

Problem 62

$800 \mathrm{gm}$ of turpentine oil is heated in a calorimeter with the help of an electric heater made of a wire having a resistance of $30 \Omega$. A voltmeter connected to the ends of the wire indicates $10 \mathrm{~V}$. After a 10 minute passage of current, turpentine is heated by $1.4^{\circ} \mathrm{C}$. The specific heat of turpentine in this experiment is
(a) $0.97 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$
(b) $9.17 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$
(c) $7.19 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$
(d) $1.79 \mathrm{~kJ} / \mathrm{kg}-\mathrm{K}$

Satpal Satpal

Numerade Educator

Problem 63

When 1 gm hydrogen $\left(\mathrm{ECE}=1.044 \times 10^{-8} \mathrm{~kg} /\right.$ coulomb $)$ forms water, $34 \mathrm{kcal}$ heat is liberated. The minimum voltage required to decompose water is
(a) $4.5 \mathrm{~V}$
(b) $3 \mathrm{~V}$
(c) $1.5 \mathrm{~V}$
(d) $0.75 \mathrm{~V}$

Satpal Satpal

Numerade Educator

Problem 64

A silver and zinc voltameter are connected in series and a current $I$ is passed through them for time $t$, liberating $W \mathrm{gm}$ of zinc. The weight of silver deposited is nearly
(a) $3.3 \mathrm{~W}$
(b) $2.4 \mathrm{~W}$
(c) $1.7 W$
(d) $\bar{W}$

Satpal Satpal

Numerade Educator

Problem 65

In an electroplating, $m$ gm of silver is deposited when 9 amp of current flows for 2 minute. The amount (in $\mathrm{gm}$ ) of silver deposited by 6 ampere of current flowing for 40 seconds will be
(a) $4 m$
(b) $m / 2$
(c) $m / 4$
(d) $2 \mathrm{~m} / 9$

Satpal Satpal

Numerade Educator

Problem 66

A certain charge liberates $0.8 \mathrm{gm}$ of oxygen. The same charge will liberate
(a) $0.8 \mathrm{gm}$ of silver
(b) $10.8 \mathrm{gm}$ of silver
(c) $108 \mathrm{gm}$ of silver
(d) $(108 / 0.8) \mathrm{gm}$ of silver

Satpal Satpal

Numerade Educator

Problem 67

ECE of $\mathrm{Cu}$ and $\mathrm{Ag}$ are $7 \times 10^{-6}$ and $1.2 \times 10^{-6} .$ A certain current deposits $14 \mathrm{~g}$ of Cu. Amount of Ag deposited is
(a) $1.2 \mathrm{~g}$
(b) $1.6 \mathrm{~g}$
(c) $2.4 \mathrm{~g}$
(d) $1.8 \mathrm{~g}$

Satpal Satpal

Numerade Educator

Problem 68

If electrochemical equivalent of hydrogen is $Z_{H} \mathrm{~kg} /$ coulequivalent and chemical equivalent of copper is $W$, then the electrochemical equivalent of copper is
(a) $Z_{H}$
(b) $Z_{H} W$
(c) $Z_{H} / W$
(d) $W / Z_{H}$

Satpal Satpal

Numerade Educator

Problem 69

A copper refining cell consists of two parallel copper plate electrodes $5 \mathrm{~cm}$ apart and 1 metre square, immersed in a copper sulphate solution of resistivity $12 \times 10^{-2} \mathrm{ohm} \times$ metre. Then the potential difference which must be established between the plates to provide a constant current to deposit $0.66 \mathrm{~kg}$ of copper on cathode in one hour is nearly (Given $Z=3.3 \times 10^{-7} \mathrm{~kg} /$ coulomb $)$.
(a) $0.6 \mathrm{~V}$
(b) $0.33 \mathrm{~V}$
(c) $3.0 \mathrm{~V}$
(d) $1.5 \mathrm{~V}$

Saman Zulfiqar

Numerade Educator

Problem 70

Two electroplating cells, one silver and another trivalent aluminium, are connected in series. After 30 minute operation, the number of silver atoms deposited to the number of aluminium atoms deposited would be:
(a) $3: 1$
(b) $1: 3$
(c) $9: 1$
(d) $1: 9$

Satpal Satpal

Numerade Educator

Problem 71

In connection with chemical effect of current, Faraday constant is equal to:
(a) electrochemical equivalent/chemical equivalent
(b) electrochemical equivalent/gram equivalent
(c) gram equivalent/electrochemical equivalent
(d) chemical equivalent/electrochemical equivalent

Satpal Satpal

Numerade Educator

Problem 72

The current inside a copper voltameter:
(a) is half the outside value
(b) is the same as the outside value
(c) is twice the outside value
(d) depends on the concentration of $\mathrm{CuSO}_{4}$

Satpal Satpal

Numerade Educator

Problem 73

ECE of copper is $3.3 \times 10^{-7} \mathrm{~kg} /$ coulomb. If $100 \mathrm{kWh}$ energy is consumed at 33 volt in a copper voltameter, then mass of copper liberated is:
(a) $3.6 \mathrm{~kg}$
(b) $3.3 \mathrm{~kg}$
(c) $1 \mathrm{~kg}$
(d) $1 \mathrm{mg}$

Satpal Satpal

Numerade Educator

Problem 74

When a copper voltameter is connected with a battery of emf 12 volt, $2 \mathrm{gm}$ of copper is deposited in 30 minute. If the same voltameter is connected across a $6 \mathrm{~V}$ battery, then the mass of the copper deposited in 45 minute would be:
(a) $1 \mathrm{gm}$
(b) $1.5 \mathrm{gm}$
(c) $2 \mathrm{gm}$
(d) $2.5 \mathrm{gm}$

Satpal Satpal

Numerade Educator

Problem 75

A mass of $0.296 \mathrm{gm}$ of copper is deposited from a solution of copper sulphate by a current of $0.5 \mathrm{amp}$ in $30 \mathrm{~min}$. The ECE of copper is:
(a) $0.00022 \mathrm{gm} / \mathrm{c}$
(b) $0.00033 \mathrm{gm} / \mathrm{c}$
(c) $0.00011 \mathrm{gm} / \mathrm{c}$
(d) $0.00066 \mathrm{gm} / \mathrm{c}$

Saman Zulfiqar

Numerade Educator

Problem 76

The degree of dissociation depends upon:
(a) concentration of electrolyte
(b) volume of electrolyte
(c) dielectric constant of electrolyte
(d) temperature of electrolyte

Satpal Satpal

Numerade Educator

Problem 77

The electrochemical equivalent of a metal is $3.3 \times 10^{-7} \mathrm{~kg}$ per coulomb. The mass of the metal liberated at the cathode when a $3 \mathrm{~A}$ current is passed for 2 seconds will be:
(a) $19.8 \times 10^{-7} \mathrm{~kg}$
(b) $9.9 \times 10^{-7} \mathrm{~kg}$
(c) $6.6 \times 10^{-7} \mathrm{~kg}$
(d) $1.1 \times 10^{-7} \mathrm{~kg}$

Satpal Satpal

Numerade Educator

Problem 78

An ammeter in series with a silver voltameter reads $0.081$ amp. If the weight of silver deposited in 20 minute is $1.071 \mathrm{gm}$, the error in the reading of ammeter is:
(ECE fo $\mathrm{Ag}=0.01118 \mathrm{gm} /$ coulomb $)$
(a) $+0.012 \mathrm{amp}$
(b) $-0.012 \mathrm{amp}$
(c) $+0.12 \mathrm{amp}$
(d) $-0.12 \mathrm{amp}$

Satpal Satpal

Numerade Educator

Problem 79

Which of the following is not the reason for the low conductivity of electrolytes?
(a) Low drift speed of ions
(b) High resistance of the solution
(c) Low number-density of charge carriers
(d) Ionisation of salt

Satpal Satpal

Numerade Educator

Problem 80

Electroplating does not help in:
(a) fine finish to the surface
(b) shining appearance
(c) metals to become hard
(d) protect metal against corrosion

Satpal Satpal

Numerade Educator

Problem 81

A copper voltameter is in series with a heater coil of resistance $0.1 \Omega$. A steady current flows in the circuit for 20 minute and a mass of $0.99 \mathrm{gm}$ of copper is deposited at the cathode. if the electrochemical equivalent of copper is $0.00033 \mathrm{gm} /$ coulomb, then heat generated in the coil is:
(a) $250 \mathrm{~J}$
(b) $350 \mathrm{~J}$
(c) $650 \mathrm{~J}$
(d) $750 \mathrm{~J}$

Satpal Satpal

Numerade Educator

Problem 82

On passing 96500 coulomb of charge through a solution of $\mathrm{CuSO}_{4}$ the amount of copper liberated is:
(a) 32 kilogram
(b) 32 gram
(c) 64 gram
(d) 64 kilogram

Satpal Satpal

Numerade Educator

Problem 83

Two ends of a conductor are at different temperatures. The electromotive force generated between the two ends is:
(a) Thomson electromotive force
(b) Peltier electromotive force
(c) Seebeck electromotive force
(d) none of the above

Satpal Satpal

Numerade Educator

Problem 84

In producing chlorine through electrolysis, 100 watt power at $125 \mathrm{~V}$ is being consumed. How much chlorine per minute is liberated? (ECE of chlorine is $0.367 \times$ $10^{-6} \mathrm{~kg} /$ coulomb $)$
(a) $13.6 \mathrm{mg}$
(b) $17.6 \mathrm{mg}$
(c) $21.3 \mathrm{mg}$
(d) $24.3 \mathrm{mg}$

Satpal Satpal

Numerade Educator

Problem 85

$x \mathrm{~g}$ of $\mathrm{Ag}$ is deposited by passing $4 \mathrm{~A}$ of current for 1 hour. How many gram of Ag will be deposited by passing $6 \mathrm{~A}$ for $40 \mathrm{~min}$ ?
(a) $2 x \mathrm{~g}$
(b) $4 x \mathrm{~g}$
(c) $\bar{x} \mathrm{~g}$
(d) $5 x \mathrm{~g}$

Satpal Satpal

Numerade Educator