IB Physics Capacitance
/A tutorial sheet on capacitance, a section in HL topic 11, is given below.
- What is the meaning of the term capacitance?
- For a given capacitor at a constant temperature, is the "capacitance" constant?
- Write down an expression for the capacitance of a charged sphere of radius R in a vacuum.
- Express the unit of capacitance in terms of SI base units.
- An uncharged capacitor of capacitance C is connected in series with an open switch across a 12 V DC battery of zero internal resistance and a resistance R. The switch is now closed. Describe the build up of charge on the capacitor.
- A capacitor of value C has a charge Q. It is connected in series to a resistor R and an open switch. The switch is now closed. Describe the current through the resistor.
- Two capacitances C1 and C2 are connected in series across a battery. Find an expression for the total capacitance. Show your working.
Two capacitances C1 and C2 are connected in parallel across a battery. Find an expression for the total capacitance. Show your working.
An uncharged capacitor is charged by being connected by wires to a battery of constant emf and zero internal resistance. (a) Is the current in the connecting wires equal to the rate of increase of charge on the plates? (b) Is there a current in the space between the plates? (c) Is there a magnetic field in the space between the plates? (d) Is the work done by the battery equal to the energy stored in the capacitor?
- In the IB Physics Data Booklet a formula is given for the capacitance of a parallel plate capacitor. What are the assumptions for this formula?
- To take into account the finite area of the plates of a capacitor see the Berkeley Physics Course Volume 2 Electricity and Magnetism by E M Purcell (red version page 97, blue version page 105) for a table of end correction values. Another reference is Physics Education, Vol 17, Number 2, March 1982, page 35.
