Can the Drude Model Explain Scattering Time in Terms of Unit Conversion?

[tigigi]

I got the answer of the hw, but still have question about it.
I need to calculate the scattering time μ = eτ / m. τ is the mean time.
the unit needs to be in cm^2 / V.S

I put the unit like this :

e = coulumb
τ = s
m = kg

then it's impossible to get the unit like that.

Then I'm wondering if I could use this to find τ and plug it in :
σ = ne^2 τ / m then

μ = σ / ne , but I got a problem that it's still not possible to solve it since we don't know the material then don't know σ.

Who could tell me what's going here. I appreciate it.

 

[Gokul43201]

I got the answer of the hw, but still have question about it.
I need to calculate the scattering time μ = eτ / m. τ is the mean time.
the unit needs to be in cm^2 / V.S

I put the unit like this :

e = coulumb
τ = s
m = kg

then it's impossible to get the unit like that.

No, it is possible. You need to convert from Coulombs to units involving volts (use the relation E =QV).

Then I'm wondering if I could use this to find τ and plug it in :
σ = ne^2 τ / m then

μ = σ / ne , but I got a problem that it's still not possible to solve it since we don't know the material then don't know σ.

Who could tell me what's going here. I appreciate it.

The Drude scattering time is a material property - it depends on the mean free path and the free electron density. We need to see the original question, exactly as it was given to you, to help with this.

 

[tigigi]

Thanks ! I'm approaching it, but there's still sth missing.

coulumb x s / kg

coulumb = J / volt , J=kg.m/s^2 -> plug in, and get

( kg.m/s^2 ) . s (1/kg) = m / v.s -> cm / v.s -> still can't get cm^2 / v.s

 

[Gokul43201]

J=kg.m/s^2

No, that's a Newton. 1J=1kg.m^2/s^2

 

[tigigi]

I really really appreciate it. I forget too many things.