1 Electric Charge and Fields Free Online FlashCards

How do electric charges interact?

Like charges repel, while unlike charges attract.

What are the charges of a proton and an electron?

A proton carries charge $+e$, an electron carries $-e$, and $e\approx1.602\times10^{-19}\,\text{C}$.

What does it mean that electric charge is quantized?

An object’s net charge is an integer multiple of the elementary charge: $q=ne$, where $n$ is an integer.

How is charge conserved during ordinary charging?

In ordinary charging, electrons transfer between objects; the total charge of an isolated system remains constant.

What is Coulomb’s law for the force magnitude between point charges?

For stationary point charges in vacuum, $F=k_e\frac{|q_1q_2|}{r^2}$, where $k_e\approx8.99\times10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$.

How do you find the net force from several source charges?

Each force acts along the line joining its two charges. With several source charges, calculate each force as a vector and add them.

What is the electric field, and what is its SI unit?

The electric field is force per unit positive test charge: $\mathbf E=\frac{\mathbf F}{q_{\text{test}}}$. Its SI unit is $\text{N/C}$.

What is the electric field of a point source charge?

A point charge produces $\mathbf E=k_e\frac{q}{r^2}\hat{\mathbf r}$, where $\hat{\mathbf r}$ points from the source charge to the field point.

Which way does an electric field point?

The field points in the direction of the force on a positive test charge; field lines point away from positive charges and toward negative charges.

How are electric fields from multiple charges combined?

Electric fields from multiple charges add as vectors. For a continuous charge distribution, sum contributions by integration.

What is electric flux through a flat surface in a uniform field?

For a flat surface in a uniform field, $\Phi_E=EA\cos\theta$, where $\theta$ is the angle between the field and the surface’s area vector.

When is electric flux through a flat surface greatest or zero?

Flux is greatest when the field is perpendicular to the surface and zero when it is parallel to the surface.