Home › ISC Class 12 › Physics › Current Electricity › Why do conduction electrons in a metal acquire a…
Why do conduction electrons in a metal acquire a steady average drift velocity even though the applied electric field continuously exerts a force on them?
AThe electric field inside the metal is zero on average
BCollisions with the fixed positive ions repeatedly randomise their motion
CThe electrons are too heavy to accelerate appreciably
DThe drift velocity exceeds the thermal speed of the electrons
Answer & Solution
Correct answer: B. Collisions with the fixed positive ions repeatedly randomise their motion
1. The field does accelerate each electron, increasing its drift speed.
2. But each electron soon collides with a positive ion and loses that gained drift speed.
3. It then accelerates again until the next collision, and so on.
4. Averaged over many collisions, electrons acquire only a steady drift speed, so B is correct; the field is non-zero (A wrong) and drift speed is far below thermal speed (D wrong).
_Source: NCERT Class 12 Physics Ch 3 "Current Electricity", p.7_
Related questions
For a battery of emf ε and internal resistance r driving current I through external resistA galvanometer of resistance G is converted into a voltmeter reading full-scale voltage V A galvanometer of resistance G shows full-scale deflection at current I_g. To convert it iThe relation between current density j, drift velocity v_d, number density n and charge e A wire has a resistance R. It is stretched uniformly so that its length becomes 2L. The neKirchhoff current law at a junction is a statement ofTwo cells of emf ε and internal resistance r each are connected in parallel. The equivalenA potentiometer of length L is used to compare emfs. If the balance lengths for cells of e