Electric Charge and Electric Force - AP Physics C Electricity and Magnetism

1. What is the direction of electric field lines around a negative charge?

   Radially inward. Negative charges attract field lines toward them.

2. What is the value of the Coulomb's constant $k$?

   $8.99 \times 10^9 \text{ N m}^2/\text{C}^2$. Also equals $\frac{1}{4\pi\epsilon_0}$, the electrostatic constant.

3. Describe the charge distribution on a conductor in electrostatic equilibrium.

   Charge resides on the surface. Charges move to the surface in electrostatic equilibrium.

4. Calculate the electric field at a point $1 \text{ m}$ from a $2 \text{ C}$ charge.

   $E = 1.8 \times 10^{10} \text{ N/C}$. Using $E = k\frac{q}{r^2} = 8.99 \times 10^9 \times \frac{2}{1^2}$.

5. How do you calculate the net force on a charge in an electric field?

   $\textbf{F} = q \textbf{E}$. Force equals charge times electric field strength.

6. Define electric charge.

   Electric charge is a property of matter that causes it to experience a force in an electric field. Fundamental property that creates electromagnetic interactions.

7. How does the electric field behave between parallel plates with opposite charges?

   Uniform field. Electric field is constant between infinite parallel plates.

8. What is the electric field strength at a point?

   $E = \frac{F}{q}$. Electric field is force per unit charge.

9. What is the direction of electric field lines around a positive charge?

   Radially outward. Positive charges create field lines pointing away from them.

10. State the formula of electric force in vector form.

    $\textbf{F} = k \frac{|q_1 q_2|}{r^2} \textbf{r}_{12}$. Unit vector $\textbf{r}_{12}$ points from $q_1$ to $q_2$.

11. What is the electric potential energy between two point charges?

    $U = k \frac{q_1 q_2}{r}$. Energy stored in the configuration of two separated charges.

12. State the relationship for potential difference in terms of field and distance.

    $V = Ed$. For uniform fields, potential difference equals field times distance.

13. What is the superposition principle as applied to electric forces?

    The net force is the vector sum of individual forces. Multiple forces add vectorially to produce net force.

14. What is the permittivity of free space $\text{ε}_0$?

    $8.85 \times 10^{-12} \text{ C}^2/(\text{N m}^2)$. Also written as $\epsilon_0$, relates to Coulomb's constant.

15. What is the electric force on a $2 \text{ C}$ charge in a $5 \text{ N/C}$ field?

    $F = 10 \text{ N}$. Using $F = qE = 2 \times 5 = 10$ N.

16. What is the electric field inside a conductor in electrostatic equilibrium?

    Zero. Free charges redistribute to cancel internal fields.

17. Define electric potential.

    Electric potential is the work done per unit charge in bringing a charge from infinity to a point in space. Energy required to assemble a charge configuration from infinity.

18. What is the relationship between electric field and electric potential?

    $E = -\nabla V$. Electric field is the negative gradient of potential.

19. Determine the resultant force on a charge located at the center of an equilateral triangle with equal charges at each corner.

    Zero. Symmetry causes all forces to cancel at the center.

20. Identify the charge of a proton.

    +1.$602 \times 10^{-19} \text{ C}$. Equal magnitude but opposite sign to electron charge.

21. What is the charge on a capacitor with a $10 \text{ V}$ potential and $2 \text{ F}$ capacitance?

    $Q = 20 \text{ C}$. Using $Q = CV = 2 \times 10 = 20$ C.

22. Find the potential energy of two $1 \text{ C}$ charges $2 \text{ m}$ apart.

    $U = 4.495 \times 10^{9} \text{ J}$. Using $U = k\frac{q_1 q_2}{r} = 8.99 \times 10^9 \times \frac{1 \times 1}{2}$.

23. What is the unit of electric field?

    Newton per Coulomb (N/C). Equivalent to volts per meter (V/m).

24. What is the principle of conservation of charge?

    The total electric charge in an isolated system remains constant. Charge cannot be created or destroyed, only transferred.

25. What does it mean when a material is a conductor?

    A conductor allows the flow of electric charge. Free electrons can move easily through the material.

26. State the formula for the electric field due to a point charge.

    $E = k \frac{|q|}{r^2}$. Field decreases with the square of distance from the charge.

27. Identify the law that states the electric flux through a closed surface is proportional to the enclosed charge.

    Gauss's Law. Relates electric flux through closed surfaces to enclosed charge.

28. State the formula for Coulomb's Law.

    $F = k \frac{|q_1 q_2|}{r^2}$. Force between two point charges is proportional to their product and inversely proportional to distance squared.

29. Define an insulator.

    An insulator is a material that resists the flow of electric charge. Electrons are tightly bound and cannot move freely.

30. What is the formula for the electric potential due to a point charge?

    $V = k \frac{q}{r}$. Potential decreases linearly with distance from the charge.

31. Calculate the work done moving a $1 \text{ C}$ charge through a $5 \text{ V}$ potential difference.

    $W = 5 \text{ J}$. Work equals charge times potential difference: $W = qV = 1 \times 5$.

32. What is the potential difference across a $2 \text{ V}$ and $3 \text{ V}$ series connection?

    $5 \text{ V}$. Potentials add algebraically in series: $2 + 3 = 5$ V.

33. State the relationship between electric potential and potential energy.

    $V = \frac{U}{q}$. Potential energy per unit charge at a point.

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