Advertisements
Advertisements
Question
Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2·5 × 10−7 m2 carrying a current of 2·7 A. Assume the density of conduction electrons to be 9 × 1028 m−3
Advertisements
Solution
We know that drift velocity,
`V_d=I/(nAq)`
where I is the current, n is charge density, q is charge of electron and A is cross-section area.
`V_d=2.7/(9xx10^28xx2.5xx10^(-7)xx1.6xx10^(-19)`
`V_d=7.5xx10^(-4) `
This is the required average drift velocity.
APPEARS IN
RELATED QUESTIONS
Write its (‘mobility’ of charge carriers) S.I. unit
When electrons drift in a metal from lower to higher potential, does it mean that all the free electrons of the metal are moving in the same direction?
Is the momentum conserved when charge crosses a junction in an electric circuit? Why or why not?
The potential difference applied across a given conductor is doubled. How will this affect (i) the mobility of electrons and (ii) the current density in the conductor? Justify your answers.
A potential difference (V) is applied across a conductor of length 'L' and cross-sectional area 'A'.
How will the drift velocity of electrons and the current density be affected if another identical conductor of the same material were connected in series with the first conductor? Justify your answers.
The drift velocity of electrons in a conductor connected to a battery is given by vd = `(−"eE" τ)/"m"`. Here, e is the charge of the electron, E is the electric field, τ is the average time between collisions and m is the mass of the electron.
Based on this, answer the following:
- How does the drift velocity change with a change in the potential difference across the conductor?
- A copper wire of length 'l' is connected to a source. If the copper wire is replaced by another copper wire of the same area of cross-section but of length '4l', how will the drift velocity change? Explain your answer.
Which expression gives the drift velocity in terms of electric field \[E\], relaxation time \[\tau\], electronic charge \[e\], and electron mass \[m\]?
What is the average velocity of electrons when no electric field is present?
Why can current be established almost instantly even when drift speed is only a few millimetres per second?
