A (i) series (ii) parallel combination of two given resistors is connected, one-by-one, across a cell. In which case will the terminal potential difference, across the cell, have a higher value?

Given, two resistors which are connected one-by-one in series and parallel combination. 

Terminal potential difference of the cell is given by,
                        V =ε-Ir 

Current across the circuit in series arrangement is given by, 
Current, Is = ER1 + R2 +r 

Current in parallel arrangement is given by,

Current, IP = ER1R2R1+R2+r  

Quite evidently,
IP > Is  Vp < Vs.

Therefore, terminal potential difference is higher in series combination as compared in parallel combination.
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Write an expression for the resistivity of a metallic conductor showing its variation over a limited range of temperatures.


The resistivity of a metallic conductor is given by
             
               ρT = ρ0 [1 + α (T – T0)]
where,
ρt is the resistivity at temperature T,
ρ0 be the resistivity at temperature T0, and
α be the temperature co-efficient.
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State the reason, why GaAs is most commonly used in making of a solar cell.

GaAs (gallium arsenide) is most commonly used in making of a solar cell because it absorbs relatively more energy from the incident solar radiations having relatively higher absorption co-efficient. Such properties are required for the fabrication of solar cells. 
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Define electromotive force of a cell.

The potential difference between two poles of a cell, when no current is drawn from it, is called electromotive force (e.m.f.) of the cell. 
Electromotive force is actually a potential difference and not a force.
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Explain how does the resistivity of a conductor depend upon (i) number density n of free electrons, and (ii) relaxation time t.

Resistivity ρ of a metal conductor is given by, 
                        ρ =mne2t

i.e.,               ρα = 1n and ρ α 1t



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