Note: You must show your work on partial-credit problems. 1. The current in an e

Question

Note: You must show your work on partial-credit problems. 1. The current in an electron beam in a cathode-ray tube is measured to be 70 microamps. How many electrons hit the screen in 5.0 seconds? a) 1.6 x 1019 b) 35 x 105 c) 3500 d) 2.2 x 1015 2. A nichrome wire has a radius of 0.50 mm and a resistivity of 15 X 10% Ohm meters. What is the resistance per unit length of this wire? 3. A increases the total number of field lines going through the surface of the balloon: charge, +Q, is placed inside a balloon and the balloon is inflated. As the radius of the balloon r a. increases proportional to r2 b. increases c. stays the same d. decreases as I/r to r . A 90V battery is connected between two parallel metal plates 4.0 mm apart. What is the magnitude of the electric field between the plates? Three capacitors of 1.0, 15, and 2.0 microfarads are connected in series. The combined capacitance about: 2.17 microfarads 46 microfarads 3 microfarads ne of these.

Explanation / Answer

1. Quantity of electricity = current in amp * time in s

Q = 70 * 10-6 * 5.0

Q = 3.50 * 10-4 C

It is known that,

Charge of 1 mol of electrons = 96500 C

SO,

96500 C = 6.022 * 1023 electrons

Then,

3.50 * 10-4 C = 3.50 * 10-4 * 6.022 * 1023 / 96500

= 2.2 * 1015 electrons

So, the answer is (d)

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