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IB DP Physics Questions

11.3 Capacitance

Question 1

Which component stores energy in an electric field when charged?

A. Resistor

B. Inductor

C. Capacitor

D. Diode

Question 2

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

Question 3

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)

Question 4

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

Question 5

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

Question 6

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]

Question 7

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]

Question 8

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]

Question 9

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]

Question 10

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]

Question 11

In a parallel combination of capacitors, which of the following is true?

A. The total capacitance is less than the smallest capacitance

B. The total capacitance is the sum of individual capacitances

C. The voltage across each capacitor is different

D. The charge on each capacitor is the same

Question 12

What happens to the energy stored in a capacitor when its capacitance is doubled, keeping the voltage constant?

A. It remains the same

B. It is halved

C. It is doubled

D. It is quadrupled

Question 13

Which of the following is a primary application of capacitors in circuits?

A. Amplification

B. Oscillation

C. Filtering

D. Rectification

Question 14

What is the effect of increasing the distance between the plates of a capacitor on its capacitance?

A. Increases the capacitance

B. Decreases the capacitance

C. No effect on the capacitance

D. Makes the capacitance negative

Question 15

In an AC circuit, how does a capacitor behave?

A. As a short circuit at low frequencies

B. As an open circuit at low frequencies

C. As a short circuit at high frequencies

D. As an open circuit at all frequencies

Question 16

a) Describe the advantages of AC transmission over DC transmission. [3]

b) In the historical context, why was DC initially preferred over AC for power distribution? [2]

c) How has the development of technology influenced the modern preference for AC transmission? [3]

Question 17

a) Explain the purpose of high voltage transmission in power grids. [3]

b) How do substations play a role in the distribution of electrical power? [2]

c) Why is safety a primary concern in the design and operation of power grids? [3]

Question 18

a) Define capacitance and state its unit. [2]

b) A capacitor is charged to a potential difference of 12 V and stores an energy of 0.036 J. Calculate the capacitance of the capacitor. [3]

c) If the same capacitor is connected to a 24 V battery, what will be the new energy stored? [3]

d) Explain why the energy stored in the capacitor increases when the potential difference is increased. [2]

Question 19

a) Describe the role of a dielectric in a capacitor. [2]

b) A capacitor with air as a dielectric has a capacitance of 2 µF. If the dielectric is changed to a material with a relative permittivity of 4, what will be the new capacitance? [3]

c) Why are dielectrics often used in capacitors even if they reduce the maximum voltage the capacitor can handle? [3]

d) Explain the phenomenon of dielectric breakdown. [2]

Question 20

a) How does the capacitance of capacitors in series compare to individual capacitances? [2]

b) Two capacitors of capacitances 4 µF and 6 µF are connected in series. Calculate the combined capacitance. [3]

c) If these capacitors were connected in parallel, what would be the combined capacitance? [2]

d) Explain why capacitors in parallel have a combined capacitance that is the sum of their individual capacitances. [2]

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