Answer to Question #192353 in Physics for King

Question

1. The electric potential in a region of uniform electric field is -1000 V at x = -0.900 m and + 

1400 V at x = + 2.00 m. What is E?

2. In a television picture tube, electrons strike the screen after being accelerated from rest through 

a potential difference of 25000 V. Ignoring relativistic effects, find the electron speed just 

before the electron strikes the screen.

3. Three point charges are fixed in place as shown in the figure below. (a) Determine the electric 

potential at point P (assuming V = 0 at infinity). (b) How much electric potential energy would 

an electron placed a point P have?

4. The current density of 1.50 A/cm2

is found in a conductor of length 10 m, when a potential 

difference of 110 V is applied across the two ends of the conductor. Calculate the conductivity 

of the wire material.

Answer 1

1. $E=\frac{\Delta\phi}{\Delta x}=\frac{1400-(-1000)}{2-(-0.9)}=828\ (V/m)$

2. $eU=mv^2/2\to v=\sqrt{2eU/m}=\sqrt{2\cdot 1.6\cdot 10^{-19}\cdot 25000/9.1\cdot10^{-31}}\approx$

$\approx94\cdot10^6\ (m/s)$

3. The picture is missing....

4. $\frac{U}{I}=\frac{\rho l}{A}\to\frac{U}{jA}=\frac{\rho l}{A}\to\rho=\frac{U}{jl}=\frac{110}{1.5\cdot 10^4\cdot10}=7.3\cdot10^{-4}\ (\Omega\cdot m)$