Question 1

A person stands inside a metal cage (as shown in the first image). What principle explains why the person is protected from external electric fields?

Accepted Answer

The cage acts as a Faraday cage, causing the electric field inside to be zero due to the redistribution of charges on the conductor's surface.

Question 2

Which equation correctly expresses Gauss’s law for the net electric flux through a closed surface?

Accepted Answer

$$\Phi_e = \frac{Q_{in}}{\$$epsilon_0$$}$$

Question 3

A parallel-plate capacitor is shown in the third image. If the area of the plate is $$A$$ and the electric field between the plates is $$E$$, what is the electric flux through a surface perpendicular to the field and between the plates?

Accepted Answer

$$\Phi_e = EA$$

Question 4

Which symmetry is required for the electric field of an infinitely long charged cylinder to be purely radial?

Accepted Answer

Cylindrical symmetry

Question 5

A box has electric field lines entering and leaving its surfaces (see image 6). If the total inward flux is 50 N·m²/C and the total outward flux is 45 N·m²/C, what is the net charge inside the box?

Accepted Answer

$$Q_{in} = -5\$$epsilon_0$$

Question 6

Which of the following statements about the electric field inside a conductor in electrostatic equilibrium is correct?

Accepted Answer

The electric field inside the conductor is zero.

Question 7

A spherical Gaussian surface surrounds a point charge $$q. $$What is the electric flux through the surface?

Accepted Answer

$$\Phi_e = \frac{q}{\$$epsilon_0$$}$$

Question 8

If a charge is placed inside a hollow cavity within a neutral conductor, what happens to the charge distribution on the conductor?

Accepted Answer

A net charge equal and opposite to the cavity charge appears on the inner surface, and an equal charge appears on the outer surface.

Question 9

A cylindrical Gaussian surface surrounds an infinite line of charge with linear charge density $$\lambda. $$What is the electric field at a distance $$r$$ from the line?

Accepted Answer

$$E = \frac{\lambda}{2\pi r \$$epsilon_0$$}$$

Question 10

A spherical Gaussian surface of radius $$r is $$placed inside a uniformly charged sphere of radius $$R$$ and total charge $$Q. $$What is the electric field at distance $$r$$ from the center (for $$r \u003c R$$)?

Accepted Answer

$$E = \frac{Qr}{4\pi \$$epsilon_0$$ R^3$}$$

Question 11

Which property of conductors in electrostatic equilibrium is established using Gauss’s law?

Accepted Answer

Any excess charge resides on the surface.

Question 12

A WiFi router cover guard (see image 10) is advertised to block electromagnetic fields. What physics principle is this device based on?

Accepted Answer

Faraday cage effect, which uses a conducting enclosure to block external electric fields.

Question 13

For a non-uniform electric field passing through a curved surface, how is the total electric flux calculated?

Accepted Answer

$$\Phi_e = \int \vec{E} \cdot d\vec{A}$$

Question 14

A spherical Gaussian surface surrounds an electric dipole. What is the net electric flux through the surface?

Accepted Answer

Zero, because the net enclosed charge is zero.

Question 15

Which of the following is true about the electric field outside a sphere of charge with total charge $$Q$$?

Accepted Answer

It is identical to the field of a point charge $$Q at $$the center.

Question 16

A charged metal sphere of radius $$R$$ has total charge $$Q. $$What is the electric field strength at its surface?

Accepted Answer

$$E = \frac{Q}{4\pi \$$epsilon_0$$ R^2$}$$

Question 17

A cylindrical Gaussian surface surrounds an infinite line of charge. What is the electric flux through the two flat ends of the cylinder?

Accepted Answer

Zero, because the electric field is radial and does not pass through the ends.

Question 18

If a surface is placed parallel to the direction of an electric field, what is the electric flux through the surface?

Accepted Answer

Zero, because the area vector is perpendicular to the field.

Question 19

Which of the following is NOT a requirement for using Gauss’s law to find the electric field easily?

Accepted Answer

The electric field must be uniform everywhere.

Ch. 24 Gauss’s Law and Electric Flux: Structured Study Notes

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