General Physics III (PHY121) - Electricity and Magnetism I

Comprehensive practice flashcards covering General Physics III lecture notes on electrostatics, Coulomb's Law, Electric Fields, and Gauss's Law.

What is the course code and title for General Physics III as per the lecture notes?

PHY121: General Physics II: Electricity and Magnetism I

What is the minimum attendance requirement for students to be eligible for the examination?

75%

According to the class rules, when is the use of laptops and other electronic devices permitted during lectures?

Strictly prohibited unless expressly permitted

What must students wear at all times during class for identification?

Their official identification cards

What is the mathematical formula for Coulomb's Law?

$$F = k \frac{q_1 q_2}{r^2}$$

What is the value and unit of Coulomb's constant (k)?

$$8.99 \times 10^9\,N\,m^2/C^2$$

How does the electric force change as the magnitude of the charge ($q$) increases?

The electric force increases

How does the electric force change as the distance ($r$) between charges increases?

The electric force decreases

What is required for the analysis of more than two charges in electrostatics?

Vector analysis

Contrast the signs allowed for electric force versus gravitational force.

Electric force can be positive or negative ($q$ can be +/-), while gravitational force must be positive ($m$ must be +)

What is the value of the gravitational constant ($G$) provided in the notes?

$$6.67 \times 10^{-11}$$

How much larger is Coulomb's constant compared to the gravitational constant according to the notes?

Almost a billion trillion times larger

What is the physical origin of the electric force?

It arises from an electric field

In which direction do electric field lines point relative to negative charges?

They point towards negative charges

In which direction do electric field lines point relative to positive charges?

They point away from positive charges

What does a higher density of electric field lines indicate about the field?

A stronger field (more lines = stronger field)

What is the magnitude of the electric force between two protons five meters apart?

$$9.2 \times 10^{-30}\,N$$

What is the definition of an electric field?

A region of space in which a charged object will experience an electrostatic force

Define the direction of the electric field line at a specific point.

The direction in which a positive charge point would accelerate when placed at that point

Do electric field lines ever cross or touch each other?

No, they never cross or touch each other

What is the orientation of electric field lines relative to the surface of a charged object?

They start and end perpendicular to the surface

Describe the field lines between two 'like' point charges.

The field lines repel each other

What is the definition of electric field strength at a point?

The electrostatic force experienced per unit positive charge placed at that point

What is the formula for electric field strength ($E$) in terms of force and charge?

$$E = \frac{F}{q}$$

What unit is equivalent to $1\,N.C^{-1}$?

$$1\,V.m^{-1}$$

What is the formula for the electric field ($E$) produced by a charge $Q$ at a distance $r$?

$$E = \frac{kQ}{r^2}$$

The electric field is directly proportional to which variable?

The magnitude of the charge ($Q$) causing the field

How is the electric field related to the distance between point charges ($r$)?

It is inversely proportional to the square of the distance ($E \propto \frac{1}{r^2}$)

If the charge changes to $5Q$ and the distance changes to $3r$, by what factor does the field strength change?

$$\frac{5}{9}$$

What is the S.I. unit of electric field according to the class work options?

$$NC^{-1}$$

What is the force on an electron of charge $q$ in an electric field of intensity $E$?

$F = qE$ opposite to the direction of the field

If air is replaced by a medium of dielectric constant $K$, what happens to the electrostatic force ($F$) between two charges?

The new force is $F/K$

What is the magnitude of electric intensity if $E = 3\mathbf{i} + 4\mathbf{j} - 2\mathbf{k}$?

$$\sqrt{29} \approx 5.4\,Vm^{-1}$$

What electric field is required to hold a $5\,mg$ oil drop with a $+10\,\mu C$ charge stationary?

$5\,Vm^{-1}$ upwards (or $5\,NC^{-1}$)

What are Gaussian surfaces?

Imaginary closed surfaces used to apply Gauss's Law

State Gauss's Law.

The total electric flux through a closed surface is proportional to the total charge enclosed within that surface

What is the formula for electric flux ($\Phi$)?

$$\Phi = EA \cos(\theta)$$

In the electric flux formula, what does $\theta$ represent?

The angle between the field and the normal to the surface

Does a charge outside a Gaussian surface affect the net flux through that surface?

No, external charges do not affect net flux through the surface

Name three shapes used as Gaussian surfaces.

Sphere, Cylinder, and Cube

Where do electric field lines terminate?

On negative charges

What is the electric field near an infinite plane sheet with surface charge density $\sigma$?

$$E = \frac{\sigma}{2\epsilon_0}$$

What is the characteristic of the electric field near an infinite plane sheet regarding distance?

It is constant and independent of distance

What is the electric flux if a uniform field of $200\,N/C$ passes through a $2\,m^2$ surface at $0^{\circ}$?

$$400\,Nm^2/C$$

What is the electric field inside a hollow conducting sphere?

Zero ($E = 0$)

Why is the electric field inside any hollow conducting surface zero?

Because all charges lie on the surface and no charges are enclosed by the internal region

What Gaussian surface is used to find the electric field of an infinite line charge?

A cylindrical Gaussian surface

What is the formula for electric field calculated in terms of potential gradient?

$$E = -\frac{dV}{dx}$$

According to the class work, what is the magnitude and direction of forces on point charge A ($-1.0\,nC$) and B ($4.0\,nC$) separated by $1.0\,cm$?

$3.6 \times 10^{-7}\,N$ (Attraction)

What does a 'ferromagnetic' object experience when placed close to a magnet?

An attractive force - the magnetic field