Electrostatics 3

Question 1

What is electric potential?

Answer 1

Electric potential is the amount of work energy needed to move a unit of electric charge from a reference point to a specific point in an electric field.

Question 2

What is the reference or zero level for measuring electric potential energies?

Answer 2

The reference or zero level is usually referred to as infinity.

Question 3

How is electric potential at a point P defined?

Answer 3

It is the work done in moving a unit positive charge from infinity to that point.

Question 4

What is the potential difference between two points?

Answer 4

It is the work done on a unit charge in moving it from one point to the other.

Question 5

What is the SI unit for electric potential and potential difference?

Answer 5

The volt (V).

Question 6

What is the relationship between volts, joules, and coulombs?

Answer 6

Volts = joules/coulombs.

Question 7

How is electrical capacity defined?

Answer 7

It is the ratio of charge stored in the conductors to the potential difference across the conductors.

Question 8

What is the function of the dielectric in a capacitor?

Answer 8

It increases the capacitance and prevents the current from flowing.

Question 8

What is electrical capacity?

Answer 8

Electrical capacity indicates the ability of a system to store charge.

Question 9

What happens when a capacitor is charging?

Answer 9

• A potential difference between the two conductive plates begins to rise.
• One plate gains excess electrons from the other plate.
• Once charging is complete, one plate has a positive charge, and the other has a negative charge.

Question 10

What happens when a capacitor is discharging?

Answer 10

• The electron excess on the negatively charged plate flows to the positively charged plate.
• This flow creates an electron flow in the circuit, acting as a voltage source.
• The flow stops when the potential difference between the plates reaches zero.

Question 11

What are some uses of capacitors in radiography?

Answer 11

• Capacitor discharge circuits
• Electronic timers
• Integrating dosimeters
• Ionization chambers

Question 12

How are capacitors used in capacitor discharge X-ray unit circuits?

Answer 12

• A capacitor is charged to the same PD as the supply.
• The power supply is disconnected.
• For radiographic exposure, the capacitor is connected across the X-ray tube.
• Electrons flow through the X-ray tube, forming an exposure.
• The capacitor discharges to almost zero based on the exposure time.