Q: A parallel plate capacitor is constructed with two plates of area $$A = 0.1\ \mathrm{m}^2$$ separated by a distance $$d = 1\ \mathrm{mm}$$, filled with air ($$\$$varepsilon_0$$ = 8.85 \times 10$$^{-12}$$\ \mathrm{F/m}). $$What is the capacitance of this capacitor?

$$C = 8.85 \times 10$$^{-10}$$\ \mathrm{F}$$

Q: A $$10\ \mu\mathrm{F}$$ and a $$20\ \mu\mathrm{F}$$ capacitor are connected in series across a $$12\ \mathrm{V}$$ battery. What is the total charge stored on the series combination?

$$4.0 \times 10$$^{-5}$$\ \mathrm{C}$$

Q: A $$5\ \mu\mathrm{F}$$ capacitor is charged to $$10\ \mathrm{V}$$ and then connected across a $$10\ \Omega$$ resistor. What is the time constant $$\tau$$ for the discharge circuit?

$$\tau = 5 \times 10$$^{-4}$$\ \mathrm{s}$$

Question 1

A parallel plate capacitor is constructed with two plates of area $$A = 0.1\ \mathrm{m}^2$$ separated by a distance $$d = 1\ \mathrm{mm}$$, filled with air ($$\$$varepsilon_0$$ = 8.85 	imes 10$$^{-12}$$\ \mathrm{F/m}). $$What is the capacitance of this capacitor?

Accepted Answer

$$C = 8.85 	imes 10$$^{-10}$$\ \mathrm{F}$$

Question 2

A bird lands on a single high-voltage power line. Why does the bird not get electrocuted?

Accepted Answer

Because both of the bird's feet are at the same electric potential, so no current flows through its body.

Question 3

Which of the following best describes the electric field just outside the surface of a conductor in electrostatic equilibrium?

Accepted Answer

It is perpendicular to the surface and proportional to the surface charge density.

Question 4

A capacitor is charged to a voltage $$V_0$$ and then disconnected from the battery. If the plates are pulled apart so that the separation doubles, what happens to the energy stored in the capacitor?

Accepted Answer

It increases by a factor of two.

Question 5

A cylindrical shell capacitor has inner radius $$a$$, outer radius $$b$$, and length $$L. $$What is the expression for its capacitance?

Accepted Answer

$$C = 2\pi\$$varepsilon_0$$ L / \ln(b/a)$$

Question 6

A $$1\ \mathrm{F}$$ capacitor is charged to $$120\ \mathrm{V}. $$How much energy is stored in the capacitor?

Accepted Answer

$$U = 7200\ \mathrm{J}$$

Question 7

Which of the following statements about the Drude model of conductivity is correct?

Accepted Answer

Electrons move with a constant drift velocity due to the electric field, interrupted by collisions.

Question 8

A resistor of $$10\ \Omega$$ and a $$5\ \Omega$$ resistor are connected in parallel. What is their equivalent resistance?

Accepted Answer

$$3.33\ \Omega$$

Question 9

A $$10\ \mu\mathrm{F}$$ and a $$20\ \mu\mathrm{F}$$ capacitor are connected in series across a $$12\ \mathrm{V}$$ battery. What is the total charge stored on the series combination?

Accepted Answer

$$4.0 	imes 10$$^{-5}$$\ \mathrm{C}$$

Question 10

A wire of length $$L$$ and cross-sectional area $$A$$ carries a current $$I. If $$the number density of free electrons is $$n$$ and the charge of an electron is $$e$$, what is the drift velocity $$v_{\mathrm{drift}} of $$the electrons?

Accepted Answer

$$v_{\mathrm{drift}} = \dfrac{I}{nAe}$$

Question 11

A $$10\ \Omega$$ resistor and a $$20\ \Omega$$ resistor are connected in series to a $$30\ \mathrm{V}$$ battery. What is the current through the circuit?

Accepted Answer

$$1.0\ \mathrm{A}$$

Question 12

A charged particle moves perpendicular to a uniform magnetic field $$\vec{B}. $$What is the path of the particle?

Accepted Answer

A circle.

Question 13

Which of the following is true about magnetic monopoles?

Accepted Answer

They do not exist; all observed magnets have both north and south poles.

Question 14

A $$5\ \mu\mathrm{F}$$ capacitor is charged to $$10\ \mathrm{V}$$ and then connected across a $$10\ \Omega$$ resistor. What is the time constant $$	au$$ for the discharge circuit?

Accepted Answer

$$	au = 5 	imes 10$$^{-4}$$\ \mathrm{s}$$

Question 15

Which of the following best describes the energy transformation in a resistor within a DC circuit?

Accepted Answer

Electrical energy is converted into thermal energy.

Question 16

A $$12\ \mathrm{V}$$ battery is connected to a circuit with three resistors in series: $$2\ \Omega$$, $$3\ \Omega$$, and $$7\ \Omega. $$What is the voltage drop across the $$3\ \Omega$$ resistor?

Accepted Answer

$$3.6\ \mathrm{V}$$

Question 17

Which of the following is NOT a correct application of Kirchhoff's rules?

Accepted Answer

The sum of the resistances in a loop must be zero.

Question 18

A proton and an electron are released from rest in a uniform electric field. Which statement is correct about their subsequent motion?

Accepted Answer

They accelerate in opposite directions; the electron has a much larger acceleration.

Question 19

A charged particle with charge $$q$$ and mass $$m$$ moves with velocity $$v$$ perpendicular to a magnetic field $$B. $$What is the radius $$r of $$its circular path?

Accepted Answer

$$r = \dfrac{mv}{qB}$$

Electric Potential, Capacitance, Circuits, and Magnetism: Structured Study Notes

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