Just wondering about electrons.

  • Thread starter Thread starter Dazed
  • Start date Start date
  • Tags Tags
    Electrons
AI Thread Summary
In a lightning bolt, approximately -20 C of charge is transferred from a cloud to the Earth, which equates to about -1.25 x 10^20 electrons using the formula N = Q/e. The discussion highlights the confusion surrounding the negative charge of electrons, as the formula suggests a negative number of electrons, which seems illogical. It clarifies that while the charge of an electron is negative, the number of electrons is considered positive when discussing quantities. The Coulomb is defined as a positive unit of charge, leading to the conclusion that the elementary charge is -1.6 x 10^-19 C for electrons. Understanding these concepts helps clarify the relationship between charge and the number of electrons involved.
Dazed
Messages
26
Reaction score
0
3. In a lightning bolt, it is estimated that a charge of -20 C is transferred from a cloud to the Earth. How many electrons make up such a lightning bolt?

N = Q/e

N = -20c / 1.6 x 10^-19

N = -1.25x10^20

I'm pretty sure this is the right answer. What I'm wondering is... how can I have a negative number of electrons? This makes this formula seem flawed to me. I guess I can just remove the negative sign after the fact, is that what most people do?
 
Physics news on Phys.org
If you are going to take e to be a positive number, then the charge of the electron has to be -e. You have a positive number of particles. Good that you recognized that your answer didn't make sense.
 
The electrical charge is either positive or negative. The Coulomb was defined as positive (since it is the amount of charge carried by 1A for one second and the current is defined as going from positive voltage to negative). So a quantity of electrons is negative since they have negative change.
 
This is the formula we were given:

Q = Ne

Where Q is the charge in coulombs, N is the number of electrons,
and e is the elementary charge (1.6 x 10^-19 C).

So the elementary charge is actually -1.6 x 10^-19 C whenever you're dealing with electrons?
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...

Similar threads

Replies
2
Views
3K
Replies
6
Views
3K
Replies
7
Views
6K
Replies
3
Views
2K
Replies
3
Views
9K
Replies
1
Views
8K
Replies
2
Views
11K
Back
Top