Explanation
At cold junction, current flows from copper to nickel and from iron to copper, and at hot junction from nickel to iron, thus the contributions add.
The filament of the heater reaches its steady resistance when the heater reaches its steady temperature, which is much higher than the room temperature. The resistance at room temperature is thus much lower than the resistance at its steady state. When the heater is switched on, it draws a larger current than its steady state current. As the filament heats up, its resistance increases and current falls to steady state value.
Cu voltameter with soluble electrodes obeys ohm’s law, In water voltameter, in the beginning when V is small (<1.7 volt), very little current flows, the voltameter does not obey ohm’s law. As soon as V exceeds 1.7 volt (back e.m.f.) the current increases steadily according to ohm’s law.
The possibility of an electric bull) fusing is higher at the time of switching ON and switching OFF because inductive effect produces a surge at the time of switching ON and OFF.
When two bulbs are connected in series, the resistance of the circuit increases and so the voltage in each decreases, hence the brightness and the temperature also decreases. Due to decrease in temperature, the resistance of the carbon filament will slightly increase while that of metal filament will decrease. Hence, carbon filament bulb will glow more brightly [P = i2R] because carbon is a semiconductor.
Neutral temperature is the temperature of hot junction, at which the thermo e.m,f. produced in the thermocouple becomes maximum. It is independent of cold junction and depends on the nature of materials of two metals used to form thermocouple.
Here assertion and reason are not correct.
The e.m.f. of a Leclanche cell falls because of the partial polarisation due to accumulation of hydrogen gas. In case Leclanche cell is used in experiment where current is drawn after short breaks, then during each break hydrogen gas escapes and Mn2O3 converts into MnO2 by taking oxygen from the atmosphere. As a result, the cell regains its original e.m.f.
When lamp B or C gets fused equivalent resistance of B and C increases. In series voltage distributes in the ratio of resistance, so voltage appearing across B increases or in other words voltage across A decreases.
When switch S is closed, bulb C is short circuited, so voltage V distributes only in two parts i.e., voltage on bulb A and B increases as compared previously. Hence illumination of bulb A and B increases.
The electrical appliances with metallic body like heater, press etc. have three pin connections. Two pins are for supply line and third pin is for earth connection for safety purposes
A laser beam is a beam of light which is light amplification by stimulated emission of radiation.
The energy per unit area of the laser beam is very high as compared to the torch light.
Follow hint of question 15 of this section.
Thomson e.m.f. in lead is practically zero.
Here Reason is not the correct explanation of the Assertion, which is correct.
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