A potential difference of V volts is applied across the ends of a copper wire of diameter D and length l. What will be the effect on drift velocity of free electrons when (i) V is doubled (ii) l is doubled?
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Drift velocity = v_drift = I / (neA) = J/(ne) = V/(neA R) = V/(neρl)
I = current n = num of electrons per unit volume (constant for copper
e = electron charge A = area of cross section = π D²/4
R = resistance of wire ρ = resistivity l = length of wire
Thus,
i) When V is doubled, drift velocity is doubled.
2) l is doubled then velocity is halved , if V remains same.
I = current n = num of electrons per unit volume (constant for copper
e = electron charge A = area of cross section = π D²/4
R = resistance of wire ρ = resistivity l = length of wire
Thus,
i) When V is doubled, drift velocity is doubled.
2) l is doubled then velocity is halved , if V remains same.
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2
Answer:
1st. doubled
2nd. half
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