#drift velocity

Potentiometer, Conductivity and Special Cases

What happens to the drift velocity of electrons in a conductor if the conductor’s temperature increases while the applie

**Potentiometer** measures potential difference without drawing current, using null deflection, principle V ∝ l, l balance length, accurate because no I r drop. Potential drop across resistor V = I R arises because electric field does work on charges, energy converted to heat, maintaining E = -dV/dx along wire. Drift velocity v_d = e E tau / m . As temperature increases, tau (relaxation time) decreases due to more collisions, reducing v_d if E is constant. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε - I r and P = I²R,

Ref: NCERT > Physics Book > Current Electricity > Potentiometer, Conductivity and Special Cases

View Details

Temperature Dependence of Resistance and Resistivity

In a conductor, if the electric field is suddenly doubled while keeping the conductor's properties unchanged, what happe

**Temperature dependence** of resistance R_t = R₀[1+α(T-T₀)], α temperature coefficient (per °C), R₀ resistance at T₀ (Ω). For metals α positive ≈10⁻³ /°C, resistance increases with temperature because τ decreases due to increased phonon scattering, n nearly constant. Drift velocity ( v_d ) is given by v_d = (e E tau/m) , where E is the electric field, e is the electron charge, tau is the relaxation time, and m is the electron mass. If E is doubled, v_d becomes 2v_d , assuming tau and other properties remain constant. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0,

Ref: NCERT > Physics Book > Current Electricity > Temperature Dependence of Resistance and Resistivity

View Details

Electric Current, Drift Velocity and Mobility

In a circuit with a battery, why does the current establish almost instantaneously when the circuit is closed, despite t

**Current and drift relation** I = n e A v_d shows current proportional to drift velocity and area. For A=6×10⁻⁷ m², I=1.8 A, n=8.5×10²⁸ m⁻³, v_d =1.8/(8.5×10²⁸×1.6×10⁻¹⁹×6×10⁻⁷)=2.2×10⁻⁴ m/s, illustrating small drift speed even for ampere currents. The electric field propagates through the conductor at near-light speed, causing all free electrons to start moving simultaneously. Drift velocity is slow, but the field’s rapid establishment initiates current instantly. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε - I r and P = I²R, evalua

Ref: NCERT > Physics Book > Current Electricity > Electric Current, Drift Velocity and Mobility

View Details

Electric Current, Drift Velocity and Mobility

Why does the drift velocity of electrons in a conductor remain constant despite continuous acceleration by an electric f

**Current and drift relation** I = n e A v_d shows current proportional to drift velocity and area. For A=6×10⁻⁷ m², I=1.8 A, n=8.5×10²⁸ m⁻³, v_d =1.8/(8.5×10²⁸×1.6×10⁻¹⁹×6×10⁻⁷)=2.2×10⁻⁴ m/s, illustrating small drift speed even for ampere currents. Electrons accelerate due to the electric field but collide with lattice ions, losing momentum. These collisions occur at random intervals, and the average time between collisions ( tau ) stabilizes the drift velocity ( v_d = e E tau / m ), balancing acceleration with energy loss. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0,

Ref: NCERT > Physics Book > Current Electricity > Electric Current, Drift Velocity and Mobility

View Details

Electric Current, Drift Velocity and Mobility

Why does the drift velocity of electrons in a conductor remain much smaller than their thermal velocity?

**Current and drift relation** I = n e A v_d shows current proportional to drift velocity and area. For A=6×10⁻⁷ m², I=1.8 A, n=8.5×10²⁸ m⁻³, v_d =1.8/(8.5×10²⁸×1.6×10⁻¹⁹×6×10⁻⁷)=2.2×10⁻⁴ m/s, illustrating small drift speed even for ampere currents. Drift velocity ( v_d = e E tau / m ) is small because E is typically weak and tau is short due to frequent collisions, whereas thermal velocity arises from random motion at high speeds (proportional to √(k T / m) ), unaffected by the field. Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε

Ref: NCERT > Physics Book > Current Electricity > Electric Current, Drift Velocity and Mobility

View Details