Physics9C‐AMidtermExam#2Winterof2020
1. Four air-gapped capacitors, C10 = 10 F, C20 = 5 F, C30 = 15 F, and C40 = 20 F
are connected as shown in the following figure. A battery maintains a potential
difference Vab = + 60 V between a and b. Initially the dielectric slab with
= 2 is not
inserted in C10.
(a) (5 points) Find the equivalent capacitance between a and b.;
(b) (10 points) Find the potential difference across C10 and C20;
(c) (10 points) Find energies stored on C20 and C30;
(d) (10 points) Maintaining the potential difference Vab = + 60 V, insert the dielectric
slab with
= 2 to fill the air-gap in C10 and make it C1. Find the potential drop
across C1 now.
(e) (Extra 10 points) For Part (d), before the dielectric slab is inserted, the capacitor
network between a and b is first disconnected from the battery. Now the dielectric
slab is inserted in C10. Find the potential drops across C1 and C40.
2. In the following circuit,
(a) (10 points) Find the direction and magnitude of the current in the circuit;
(b) (5 points) Find the energy dissipated in the 5 resistor;
(c) (5 points) Find the potential difference Vad = Va – Vd.
