11.3 Capacitance

Which component stores energy in an electric field when charged?

A. Resistor

B. Inductor

C. Capacitor

D. Diode

What is the primary function of a dielectric material in a capacitor?

A. To allow current flow between the plates

B. To increase the capacitance

C. To decrease the voltage

D. To act as a resistor

Two capacitors of capacitances C1 and C2 are connected in series. Which of the following represents their combined capacitance?

A. C1 + C2

B. C1 x C2

C. 1/C1 + 1/C2

D. (C1 x C2) / (C1 + C2)

A capacitor is being charged through a resistor. What happens to the current as the capacitor charges?

A. It increases

B. It decreases

C. It remains constant

D. It becomes zero immediately

Which of the following best describes the time constant of an RC circuit?

A. The time taken for the voltage across the capacitor to reach half its maximum value

B. The time taken for the current to become zero

C. The time taken for the voltage across the capacitor to reach approximately 63% of its maximum value

D. The time taken for the capacitor to fully discharge

a) Explain the role of dielectrics in capacitors and how they influence the capacitance of a capacitor. [3]

b) A capacitor with a dielectric has a capacitance of 5 µF. When the dielectric is removed, its capacitance drops to 2 µF. Calculate the relative permittivity (dielectric constant) of the dielectric material. [2]

a) Describe the process of charging a capacitor in terms of current flow and voltage buildup. [3]

b) If a 12 V battery is used to charge a 4 µF capacitor, calculate the amount of energy stored in the capacitor once fully charged. [2]

a) Explain the concept of time constant in relation to the discharging of a capacitor through a resistor. [3]

b) A capacitor of capacitance 8 µF is discharged through a 500 kΩ resistor. Calculate the time constant for this RC circuit. [2]

a) Describe the construction of a parallel plate capacitor and explain the significance of the plate area and separation distance in determining its capacitance. [3]

b) A parallel plate capacitor has a plate area of 0.02 m^2 and a separation distance of 2 mm. If the dielectric between the plates has a relative permittivity of 5, calculate the capacitance of this capacitor. [3]

c) How would the capacitance change if the separation distance is halved? [2]

a) Explain the difference between a step-up and a step-down transformer. [2]

b) A step-down transformer has 500 turns on the primary coil and 100 turns on the secondary coil. If the primary voltage is 240 V, what is the secondary voltage? [3]

c) Why are step-down transformers commonly used in household electrical systems? [2]