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Subject: Physics    / General Physics
Question

Section 4

1. (a) (1/2 point) How does the shape of the foil affect the capacitance? Would it still be a capacitor if the foil and mylar took on a different shape; say for example if the top sheet of foil were crumpled into a ball?

(b) (1/2 point) How much do the lead wires of the LCR meter contribute and how much does this value vary with their position? When the LCR meter is connected to the foil capacitor is the capacitence contributed by the wire leads additive? If so why?

How much do the lead wires of the LCR meter contribute:

and how much does this value vary with their position?

When the LCR meter is connected to the foil capacitor is the capacitence contributed by the wire leads additive? If so why?

(c) (1/2 point) Approximate how much energy is being stored in your capacitor. Neglecting fringing, what is the strength of the electric field storing this energy?

Section 5

2. (a) (1/2 point) Solve for your best guess of the capacitance with and without the mylar sheet. How do these two values of capacitance compare? Which one is larger; is this what you expected?

(b) (1=2 point) It is a good approximation to assume the relative permittivity of air is 1 (actual value of 1.00059), thus as a dielectric it behaves essentially like vacuum, for our purposes. Therefore assuming the capacitor without the acrylic slab has a relative permittivity of one (?r = 1) then, based on your Capacitance measurements and the fact that the geometry stayed the same, calculate the relative permittivity of the acrylic slab (hint: Use Eq. 3 and your second capacitance measurement to solve for the term ?0A/d. This should be constant for both measurements).

(c) (1/2 point) Discuss the effects of fringing of the fields. Why is Eq. 3 an approximation to the capacitance of a parallel plate capacitor?

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Section 7

3. (1/2 point) Compare the recorded times: How does the change in resistance compare to the change in time it took to dim the bulb (Note the bulb also contributes to the total resistance of the circuit)? When is current maximal/minimal?