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State whether an electric heater will consume more electrical energy or less electrical energy per second when the length of its heating element is reduced. Give reason for your answer.

(a) what is the rate at which energy being delivered to a light bulb higher : just after it is turned on , the glow of the filament is increasing , or after it has been on for a few seconds and the glow is steady ? (b) IF a piece of wire is used to connect points b and c in Fig. 7.9, does the brightness of bulb R_(1) increase , decrease or stay constant ? What happens to the brightness of bulb R_(2) ? (I_(1) = I_(2) = I) (c) Compare the brightness of four identical light bulbs in Fig. 7.10 . What happens if the bulb A fails so that it cannot conduct ? What if C fails ? What if D fails? (d) If electric power is transmitted over long distances, the resistance of the wires becomes significant. Why ? Which mode of transmission would result in less energy losss: high current and low voltage or low current and high voltage ? Discuss. (e) In Fig. 7.11 , describe wha happens to the light bulb after the switch is closed . Assume the capacitor has a large capacitance and is initially uncharged. (f) Astuident claims that a second light bulb in series is less bright than the first , because the first bulb uses up some of the current . How would you respond to this statement ? (g) If you were to design an electeric heater using nichrome wire as the heating element , what parameters of the wire would you vary to meet a specific power output , sch as 1000 W ?

(a) what is the rate at which energy being delivered to a light bulb higher : just after it is turned on , the glow of the filament is increasing , or after it has been on for a few seconds and the glow is steady ? (b) IF a piece of wire is used to connect points b and c in Fig. 7.9, does the brightness of bulb R_(1) increase , decrease or stay constant ? What happens to the brightness of bulb R_(2) ? (I_(1) = I_(2) = I) (c) Compare the brightness of four identical light bulbs in Fig. 7.10 . What happens if the bulb A fails so that it cannot conduct ? What if C fails ? What if D fails? (d) If electric power is transmitted over long distances, the resistance of the wires becomes significant. Why ? Which mode of transmission would result in less energy losss: high current and low voltage or low current and high voltage ? Discuss. (e) In Fig. 7.11 , describe wha happens to the light bulb after the switch is closed . Assume the capacitor has a large capacitance and is initially uncharged. (f) Astuident claims that a second light bulb in series is less bright than the first , because the first bulb uses up some of the current . How would you respond to this statement ? (g) If you were to design an electeric heater using nichrome wire as the heating element , what parameters of the wire would you vary to meet a specific power output , sch as 1000 W ?

(a) What is meant by saying that the potential difference two points is 1 volt ? Name a device that helps to measure the potential difference across a conductor. (b) Why does the connecting cord of an electric heater not glow hot while the heating element does ? ( c) Electrical resistivities of some substances at 20^@ C are given below : Silver 1.60 xx 10^-8 Omega m Copper 1.62 xx 10^-8 Omega m Tungsten 5.20 xx 10^-8 Omega m Iron 10.0 xx 10^-8 Omega m Mercury 94.0 xx 10^-8 Omega m Nichrome 100 xx 10^-6 Omega m . Answer the following question in relation to them : (i) Among silver and copper, which one is a better conductor ? Why ? (ii) Which material would you advise to be used in electrical heating devices ? Why ?

(a) Two heater coils made of the same material are connected in paralled across the mains. The length of diameter of one the coil is triple that of other. Which of these will produce more heat? (b) Three equal resistors connected in series across a source of emf together dissipated 10 Watt of power. What would be the power disspated if the same resistors are connected in parallel across the same source of emf? Two resistor R_(1) and R_(2) may be connect either in series or in parellel across a battery of zero internal resistance. it is required that joule heating for the parallel combination be four times than for series combination. if R_(1)= 100 Omega find R_(2) (d) The three resistance A, B and C have values 3R, 6R and R respectively. Now some potential difference is applied across the network . Find the ratio of thermal powers dissipated between X and Y . find ratio of power consumed by A,B, and C .

Following experiment was performed by J.J. Thomson in order to measure ratio of charge e and mass m of electron. Electrons emitted from a hot filament are accelerated by a potential difference V. As the electrons pass through deflecting plates, they encounter both electric and magnetic fields. the entire region in which electrons leave the plates they enters a field free region that extends to fluorescent screen. The entire region in which electrons travel is evacuated. Firstly, electric and magnetic fields were made zero and position of undeflected electron beam on the screen was noted. The electric field was turned on and resulting deflection was noted. Deflection is given by d_(1) = (eEL^(2))/(2mV^(2)) where L = length of deflecting plate and v = speed of electron. In second part of experiment, magnetic field was adjusted so as to exactly cancel the electric force leaving the electron beam undeflected. This gives eE = evB . Using expression for d_(1) we can find out (e)/(m) = (2d_(1)E)/(B^(2)L^(2)) A beam of electron with velocity 3 xx 10^(7) m s^(-1) is deflected 2 mm while passing through 10 cm in an electric field of 1800 V//m perpendicular to its path. e//m for electron is

Following experiment was performed by J.J. Thomson in order to measure ratio of charge e and mass m of electron. Electrons emitted from a hot filament are accelerated by a potential difference V. As the electrons pass through deflecting plates, they encounter both electric and magnetic fields. the entire region in which electrons leave the plates they enters a field free region that extends to fluorescent screen. The entire region in which electrons travel is evacuated. Firstly, electric and magnetic fields were made zero and position of undeflected electron beam on the screen was noted. The electric field was turned on and resulting deflection was noted. Deflection is given by d_(1) = (eEL^(2))/(2mV^(2)) where L = length of deflecting plate and v = speed of electron. In second part of experiment, magnetic field was adjusted so as to exactly cancel the electric force leaving the electron beam undeflected. This gives eE = evB . Using expression for d_(1) we can find out (e)/(m) = (2d_(1)E)/(B^(2)L^(2)) A beam of electron with velocity 3 xx 10^(7) m s^(-1) is deflected 2 mm while passing through 10 cm in an electric field of 1800 V//m perpendicular to its path. e//m for electron is

A well insulated container has a mixture of ice and water, at 0^(@)C . The mixture is supplied heat at a constant rate of 420 watt by switching on an electric heater at time t = 0. The temperature of the mixture was recorded at time t = 150s, 273s and 378s and the readings were 0^(@)C , 10^(@)C and 20^(@)C respectively. Calculate the mass of water and ice in the mixture. Specific heat of water = 4.2 J g^(-1) .^(@)C^(-1) , Specific latent heat of fusion of ice = 336 J g^(-1) . Assume that the mixture is stirred slowly to maintain a uniform temperature of its content.