Electrical Power & Heating Effect

A room heater is rated $400\text{ W}, 220\text{ V}$. If the supply voltage drops to 200 V, what will be the power consumed (approximately)?

An electric power line having total resistance of $2\ \Omega$, delivers 1 kW of power at 250 V. The percentage efficiency of transmission line is ______.

Refer to the circuit diagram given below. The heat generated across the $6\ \Omega$ resistance in 100 second is $\frac{\alpha}{100}\text{ J}$. The value of $\alpha$ is ______. (Nearest integer)

The heat generated in 1 minute between points $A$ and $B$ in the given circuit, when a battery of 9 V with internal resistance of $1\ \Omega$ is connected across these points is ______ J.

Two resistors of 200 $\Omega$ and 400 $\Omega$ are connected in series with a battery of 100 V. A bulb rated at 200 V, 100 W is connected across the 400 $\Omega$ resistance. The potential drop across the bulb is ________ V.

A motor operating on 100 V draws a current of 1 A. If the efficiency of the motor is $91.6\%$, then the loss of power in units of $\text{cal/s}$ is

The battery of a mobile phone is rated as $4.2\text{ V},\ 5800\text{ mAh}$. How much energy is stored in it when fully charged?

There are ' $n$ ' number of identical electric bulbs, each is designed to draw a power $p$ independently from the mains supply. They are now joined in series across the mains supply. The total power drawn by the combination is:

The current flowing in a coil is 3 A and the power consumed is 108 W. If the a.c. source is of $120\text{ V}, 50\text{ Hz}$, the resistance in the circuit is

An electric bulb rated $50\text{ W} - 200\text{ V}$ is connected across a $100\text{ V}$ supply. The power dissipation of the bulb is:

In the following circuit, a power of 50 watt is absorbed in the section AB of the circuit. The value of resistance ' $x$ ' is

In the following circuit, the battery has an emf of $2\text{ V}$ and an internal resistance of $\frac{2}{3}\ \Omega$. The power consumption in the entire circuit is _________ W.

The ratio of heat dissipated per second through the resistance $5\ \Omega$ and $10\ \Omega$ in the circuit given below is:

When a potential difference $V$ is applied across a wire of resistance $R$, it dissipates energy at a rate $W$. If the wire is cut into two halves and these halves are connected mutually parallel across the same supply, the energy dissipation rate will become:

Two heaters $A$ and $B$ have power rating of $1\text{ kW}$ and $2\text{ kW}$, respectively. Those two are first connected in series and then in parallel to a fixed power source. The ratio of power outputs for these two cases is:

Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be _________ to __________ times of its initial length if the water is to be boiled in 15 minutes.

By what percentage will the illumination of the lamp decrease if the current drops by 20%?

A heater is designed to operate with a power of $1000\text{ W}$ in a $100\text{ V}$ line. It is connected in combination with a resistance of $10\ \Omega$ and a resistance $R$, to a $100\text{ V}$ mains as shown in figure. For the heater to operate at $62.5\text{ W}$, the value of $R$ should be _______ $\Omega$.

The $\mathrm{H}$ amount of thermal energy is developed by a resistor in $10\text{ s}$ when a current of $4\text{ A}$ is passed through it. If the current is increased to $16\text{ A}$, the thermal energy developed by the resistor in $10\text{ s}$ will be:

Ratio of thermal energy released in two resistors R and 3R connected in parallel in an electric circuit is:

Two identical heater filaments are connected first in parallel and then in series. At the same applied voltage, the ratio of heat produced in same time for parallel to series will be:

Different combination of 3 resistors of equal resistance $R$ are shown in the figures. The increasing order for power dissipation is:

A potential $V_0$ is applied across a uniform wire of resistance $R$. The power dissipation is $P_1$. The wire is then cut into two equal halves and a potential of $V_0$ is applied across the length of each half. The total power dissipation across two wires is $P_2$. The ratio $P_2 : P_1$ is $\sqrt{x} : 1$. The value of $x$ is ___________.

Two resistors of resistance, 100 $\Omega$ and 200 $\Omega$ are connected in parallel in an electrical circuit. The ratio of the thermal energy developed in 100 $\Omega$ to that in 200 $\Omega$ in a given time is

A resistor develops 300 J of thermal energy in 15 s, when a current of 2 A is passed through it. If the current increases to 3 A, the energy developed in 10 s is ____________ J.

An electrical bulb rated 220 V, 100 W, is connected in series with another bulb rated 220 V, 60 W. If the voltage across combination is 220 V, the power consumed by the 100 W bulb will be about _______ W.

Two coils require 20 minutes and 60 minutes respectively to produce same amount of heat energy when connected separately to the same source. If they are connected in parallel arrangement to the same source; the time required to produce same amount of heat by the combination of coils, will be ___________ min.

A resistor develops 500 J of thermal energy in 20 s when a current of 1.5A is passed through it. If the current is increased from 1.5A to 3A, what will be the energy developed in 20 s.

A uniform heating wire of resistance 36$\Omega$ is connected across a potential difference of 240 V. The wire is then cut into half and potential difference of 240V is applied across each half separately. The ratio of power dissipation in first case to the total power dissipation in the second case would be 1: x, where x is ____________

A resistor dissipates 192 J of energy in 1s when a current of 4A is passed through it. Now, when the current is doubled, the amount of thermal energy dissipated in 5s in _________ J.

The energy dissipated by a resistor is 10 mJ in 1 s when an electric current of 2 mA flows through it. The resistance is ___________$\Omega$. (Round off to the Nearest Integer)

In an electrical circuit, a battery is connected to pass 20C of charge through it in a certain given time. The potential difference between two plates of the battery is maintained at 15V. The workdone by the battery is __________J.

In the given figure, the emf of the cell is 2.2 V and if internal resistance is 0.6$\Omega$. Calculate the power dissipated in the whole circuit:

An electric bulb of 500 watt at 100 volt is used in a circuit having a 200 V supply. Calculate the resistance R to be connected in series with the bulb so that the power delivered by the bulb is 500 W.

An electric bulb rated as 200 W at 100 V is used in a circuit having 200 V supply. The resistance 'R' that must be put in series with the bulb so that the bulb delivers the same power is _____________ $\Omega$.

If a current flowing in a coil is reduced to half of its initial value, the relation between the new energy $(E_2)$ and the original energy $(E_1)$ stored in the coil will be

Due to cold weather a 1 m water pipe of cross-sectional area 1 cm2 is filled with ice at $-10^\circ$C. Resistive heating is used to melt the ice. Current of 0.5A is passed through 4 k$\Omega$ resistance. Assuming that all the heat produced is used for melting, what is the minimum time required? (Given latent heat of fusion for water/ice = 3.33 $\times$ 105 J kg${}^{-1}$, specific heat of ice = 2 $\times$ 103 J kg${}^{-1}$ and density of ice = 103 kg/m3)

An electrical power line, having a total resistance of 2 $\Omega$, delivers 1 kW at 220 V. The efficiency of the transmission line is approximately:

In a building there are 15 bulbs of 45 W, 15 bulbs of 100 W, 15 small fans of 10 W and 2 heaters of 1 kW. The voltage of electric main is 220 V. The minimum fuse capacity (rated value) of the building will be:

Two equal resistances when connected in series to a battery, consume electric power of 60 W. If these resistances are now connected in parallel combination to the same battery, the electric power consumed will be:

Which of the following acts as a circuit protection device?

A current of 2 mA was passed through an unknown resistor which dissipated a power of 4.4 W. Dissipated power when an ideal power supply of 11 V is connected across it is -

Six similar bulbs are connected as shown in the figure with a DC source of emf E, and zero internal resistance.

The ratio of power consumption by the bulbs when (i) all are glowing and (ii) in the situation when two from section A and one from section B are glowing, will be:

Two electric bulbs, rated at (25 W, 220 V) and (100 W, 220 V), are connected in series across a 220 V voltage source. If the 25 W and 100 W bulbs draw powers P1 and P2 respectively, then:

A constant voltages is applied between two ends of a metallic wire. If the length is halved and the radius of the wire is doubled, the rate of heat developed in the wire will be:

The figure shows three circuits I, II and III which are connected to a 3V battery. If the powers dissipated by the configurations I, II and III are P1, P2 and P3 respectively, then:

A filament bulb (500 W, 100 V) is to be used in a 230 V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is

The charge flowing through a resistance R varies with time t as Q = at $-$ bt2, where $a$ and $b$ are positive constants. The total heat produced in R is

Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 $\Omega$. The power loss in the wire is

Four bulbs B1, B2, B3 and B4 of 100 W each are connected to 220 V main as shown in the figure. The reading in an ideal ammeter will be:

In a large building, there are $15$ bulbs of $40\text{ W},\ 5$ bulbs of $100\text{ W},\ 5$ fans of $80\text{ W}$ and $1$ heater of $1\text{ kW}.$ The voltage of electric mains is $220\text{ V}.$ The minimum capacity of the main fuse of the building will be:

Which of the four resistances P, Q, R and S generate the greatest amount of heat when a current flows from A to B?

Ten identical cells connected in series are needed to heat a wire of length one meter and radius 'r' by 10oC in time 't'. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time 't'?

The supply voltage to room is $120\text{ V}.$ The resistance of the lead wires is $6\ \Omega$. A $60\text{ W}$ bulb is already switched on. What is the decrease of voltage across the bulb, when a $240\text{ W}$ heater is switched on in parallel to the bulb?

If voltage across a bulb rated 220 volt-100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is

The power dissipated in the circuit shown in the figure is 30 watts. The value of R is

Two electric bulbs marked $25\text{ W} - 220\text{ V}$ and $100\text{ W} - 220\text{ V}$ are connected in series to a $440\text{ V}$ supply. Which of the bulbs will fuse?

If power dissipated in the 9 $\Omega$ resistor in the circuit shown is 36 watt, the potential difference across the 2 $\Omega$ resistor is

A thermocouple of negligible resistance produces an e.m.f. of 40 µV/ºC in the linear range of temperature. A galvanometer of resistance 10 ohm whose sensitivity is 1 µA/division, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be

The thermo e.m.f. $E$ in volts of a certain thermo-couple is found to vary with temperature difference $\theta$ in °C between the two junctions according to the relation

$E = 30\theta - \frac{\theta^2}{15}$

The neutral temperature for the thermo-couple will be

In producing chlorine by electrolysis $100\text{ kW}$ power at $125\text{ V}$ is being consumed. How much chlorine per minute is liberated (E.C.E. of chlorine is $0.367 \times 10^{-6}\text{ kg/C}$)

A current of 3 amp. flows through the 2 $\Omega$ resistor shown in the circuit. The power dissipated in the 5 $\Omega$ resistor is

An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20oC? The temperature of boiling water is 100oC

A steady current of 1.5 amp flows through a copper voltameter for 10 minutes. If the electrochemical equivalent of copper is $30 \times 10^{-5}\text{ g coulomb}^{-1}$, the mass of copper deposited on the electrode will be

If the cold junction of a thermocouple is kept at $0^\circ\text{C}$ and the hot junction is kept at $T^\circ\text{C}$, then the relation between neutral temperature $(T_n)$ and temperature of inversion $(T_i)$ is

The total power dissipated in watt in the circuit shown here is

An electric bulb is rated $220$ volt - $100$ watt. The power consumed by it when operated on $110$ volt will be

A thermocouple is made from two metals, Antimony and Bismuth. If one junction of the couple is kept hot and the other is kept cold, then, an electric current will

Power dissipated across the 8 $\Omega$ resistor in the circuit shown here is 2 watt. The power dissipated in watt units across the 3 $\Omega$ resistor is

In producing chlorine through electrolysis $100\text{ W}$ power at $125\text{ V}$ is being consumed. How much chlorine per min is liberated? ECE of chlorine is $0.367 \times 10^{-6}\text{ kg/C}$

A 5-ampere fuse wire can withstand a maximum power of 1 watt in the circuit. The resistance of the fuse wire is

A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be

The temperature of inversion of a thermocouple is $620^\circ\text{C}$ and the neutral temperature is $300^\circ\text{C}$. What is the temperature of cold junction?

The resistance of hot tungsten filament is about $10$ times the cold resistance. What will be resistance of $100\text{ W}$ and $200\text{ V}$ lamp when not in use?

Two voltmeters, one of copper and another of silver, are joined in parallel. When a total charge $q$ flows through the voltmeters, equal amount of metals are deposited. If the electrochemical equivalents of copper and silver are $Z_1$ and $Z_2$ respectively the charge which flows through the silver voltmeter is

when three identical bulbs of 60 watt, 200 volt rating are connected in series to a 200 volt supply, the power drawn by them will be

In India electricity is supplied for domestic use at 220 V. It is supplied at 110 V in USA. If the resistance of a 60 W bulb for use in India is R, the resistance of a 60 W bulb for use in USA will be

The electrochemical equivalent of a metal is $3.3 \times 10^{-7}\text{ kg}$ per Coulomb. The mass of the metal liberated at the cathode when a $3\text{ A}$ current is passed for $2$ seconds will be

A battery is charged at a potential of 15 V for 8 h when the current flowing is 10 A. The battery on discharge supplies a current of 5 A for 15 h. The mean terminal voltage during discharge is 14 V. The "watt-hour" efficiency of the battery is

The thermo $\text{emf}$ of a thermocouple varies with temperature $\theta$ of the hot junction as $E = a\theta + b\theta^2$ in volts where the ratio $a/b$ is $700^\circ\text{C}.$ If the cold junction is kept at $0^\circ\text{C},$ then the neutral temperature is

Two 220 volt, 100 watt bulbs are connected first in series and then in parallel. Each time the combination is connected to a 220 volt a.c. supply line. The power drawn by the combination in each case respectively will be

Fuse wire is a wire of

A $220$ volt, $1000$ watt bulb is connected across a $110\text{ volt}$ mains supply. The power consumed will be

An electric kettle has two heating coils. When one of the coils is connected to an a.c. source, the water in the kettle boils in 10 minutes. When the other coil is used the water boils in 40 minutes. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be

The thermo $\text{e.m.f.}$ of a thermo -couple is $25\ \mu\text{V}/^\circ\text{C}$ at room temperature. A galvanometer of $40\text{ ohm}$ resistance, capable of detecting current as low as $10^{-5}\text{ A},$ is connected with the thermo couple. The smallest temperature difference that can be detected by this system is

The negative $\text{Zn}$ pole of a Daniell cell, sending a constant current through a circuit, decreases in mass by $0.13\text{ g}$ in $30$ minutes. If the electrochemical equivalents of $\text{Zn}$ and $\text{Cu}$ are $32.5$ and $31.5$ respectively, the increase in the mass of the positive $\text{Cu}$ pole in this time is

A wire when connected to $220\text{ V}$ mains supply has power dissipation $P_1.$ Now the wire is cut into two equal pieces which are connected in parallel to the same supply. Power dissipation in this case is $P_2.$ Then $P_2 : P_1$ is

The mass of product liberated on anode in an electrochemical cell depends on (where $t$ is the time period for which the current is passed).

If $\theta_i$ is the inversion temperature, $\theta_n$ is the neutral temperature, $\theta_c$ is the temperature of the cold junction, then

If in the circuit, power dissipation is $150\text{ W},$ then $R$ is

Two bulbs of (40 W, 200 V), and (100 W, 200 V). Then correct relation for their resistances

In electrolysis the mass deposited on an electrode is directly proportional to

Three equal resistors connected in series across a source of emf together dissipate $10$ watt of power. What will be the power dissipated in watt if the same resistors are connected in parallel across the same source of emf?

A $5^\circ\text{C}$ rise in temperature is observed in a conductor by passing a current. When the current is doubled the rise in temperature will be approximately

If nearly $10^{5}\text{ C}$ liberate $1\text{ g}$ equivalent of aluminium, then the amount of aluminium (equivalent weight 9) deposited through electrolysis in $20\text{ min}$ by a current of $50$ amp will be

One kilowatt hour is equal to

A (100 W, 200 V) bulb is connected to a 160 volts supply. The power consumption would be

If two bulbs, whose resistances are in the ratio of $1 : 2$ are connected in series, the power dissipated in them has the ratio of

A heating coil is labelled 100 W, 220 V. The coil is cut in half and the two pieces are joined in parallel to the same source. The energy now liberated per second is

An electric bulb is rated 60 W, 220 V. The resistance of its filament is

A current of $2\text{ A}$, passing through a conductor produces $80\text{ J}$ of heat in 10 seconds. The resistance of the conductor in ohm is

40 electric bulbs are connected in series across a $220\text{ V}$ supply. After one bulb is fused the remaining 39 are connected again in series across the same supply. The illumination will be