Question 1 If an electron travels 0.300 m from an electron gun to a TV screen in

Question

Question 1

If an electron travels 0.300 m from an electron gun to a TV screen in 18.0 ns, what voltage was used to accelerate it? (Note that the voltage you obtain here is lower than actually used in TVs to avoid the necessity of relativistic corrections.)

Question 2

The voltage across a membrane forming a cell wall is 74.0 mV and the membrane is 8.80 nm thick. What is the electric field strength? (The value is surprisingly large, but correct. Membranes are discussed in Section 19.7* of the textbook.) You may assume a uniform E-field.

Explanation / Answer

Question 1

If an electron travels 0.300 m from an electron gun to a TV screen in 18.0 ns, what voltage was used to accelerate it? (Note that the voltage you obtain here is lower than actually used in TVs to avoid the necessity of relativistic corrections.)

y = 0.5 a t^2

==> a = 2y/t^2 = 2*0.300/(18e-9*18e-9) = 1.8519e15 m/s2

F = m a = 9.109e-31 * 1.8519e15 = 1.6869e-15 N

E = F/q = 1.6869e-15/1.6e-19 = 10543 N/C

V = E d = 10543 * 0.3 = 3162.9 = 3160 V

Question 2

The voltage across a membrane forming a cell wall is 74.0 mV and the membrane is 8.80 nm thick. What is the electric field strength? (The value is surprisingly large, but correct. Membranes are discussed in Section 19.7*of the textbook.) You may assume a uniform E-field.

E = V/d = 74e-3/8.8e-9 = 8.41 x 10^6 N/C

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