Thursday Feb 4:

 

Journal:

Point P is 2.50 meters from a point charge of

20.0 x 10-8 coulomb.

 

1) What is the intensity of the electric field at Point P ?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Answer:  (E = kq/r2)  à (9x109) (20.0 x 10-8)/ (2.5)2

 = 28.8 x 101 N/C à 2.88 x102 N/C  or V/m

E = Newtons per Coulomb (N/C) is also expressed as

            Volts per meter (V/m)

 

2) What is the electric potential at Point P ?

 

 

 

 

 

 

 

 

 

   E = V/d

à V = Ed à (2.88x 102)(2.50) = 720 volts

 

 

 

 

 

 

 

 

Quiz: Capacitors

The following questions will be a quiz on this Friday

 

 

 

 

 

 

 

 

 

       

                                                                                      

1. The voltage across the 5mF capacitor is?

2. The voltage across the right side circuit (A --> C) is?

3. The equivalent capacitance for the 4 microfarad (mF) & the 2mF parallel capacitors is?

4. The equivalent capacitance for the three capacitors (4mF, 2mF & 3mF) on the right side (Aà C)?

 

5.  What is the difference in electrical potential between points:

            a. A and D

Capacitors in a series all have the same charge. It takes twice the voltage to keep its charge in the 3mF as the two capacitors in parallel (6mF as compared to the 3mF capacitor). Total voltage from A to C is 100V. So,  

1/3 of 100V = 33.3V  (from A to D)

   

b. D and C

 

6. The equivalent capacitance for this network is most nearly?

 

7.  A) The charge stored in the 5‑microfarad capacitor?

Q = CV

      B) The charge in the 4mF capacitor?

      C) The charge in the 2mF capacitor?

       D) The charge in the 3mF capacitor?

 

8. What is the PE of the 5‑microfarad capacitor? 

1/2(CV2)

 

9. A parallel-plate capacitor has a capacitance C1.  A second parallel-plate capacitor (same dielectric constant Eo) has plates with 10 times the area and 5 times the separation.  The capacitance of the second capacitor (C2) is most nearly

C1 = EoA1/d1

C2 = Eo10A1/5d1

 

10. Ten Joules of work is needed to move 2 coulombs of charge from one point to another (1m) with no change in velocity. 

a.  What is the change in electrical potential?

 W = DVq 

    b. What is the change in potential energy?   

      W = DPE = q DV 

c.  What is the electric field strength?

E = volts per meter (V/m)

 

 

 

 

 

 

 

 

11. Two large parallel conducting plates -Q and Q are connected to a battery of emf  

       12V, as shown above.

a. Does the force at various distances between the plates?

b. Does the potential at various distances between the plates?  If so, where is it the highest & lowest potential?

 

 

12.  

  

 

 

 

 

 

 

 

 

12. Three identical resistors (10W), and a capacitor of 1.0 x 10-9 F are connected to

a 30 V battery, as shown in the circuit diagram above. Switches S1 and S2 are initially closed, and switch S3 is initially open. A voltmeter is connected as shown. Find:

a. Current through the battery

b. Determine the reading on the voltmeter.

c. Switches S1 and S2 are now opened, and then switch S3 is closed. Determine the charge Q on the capacitor after S3 has been closed for a long time.