Electric Current - AP Physics C Electricity and Magnetism

1. If $Q = 10 \, C$ and $t = 5 \, s$, find the current $I$.

   $I = 2 \, A$. Apply $I = \frac{Q}{t} = \frac{10}{5} = 2$ A.

2. What is the meaning of direct current (DC)?

   Current flows in one direction. Current maintains constant direction over time.

3. What is the unit of electric current?

   Ampere (A). Standard SI unit for electric current flow.

4. What does $I$ represent in the formula $I = \frac{Q}{t}$?

   Electric current. Symbol for electric current in equations.

5. What does $n$ represent in $I = nAve$?

   Number of charge carriers per unit volume. Density of free electrons in the material.

6. State the formula for electric current.

   $I = \frac{Q}{t}$. Current equals charge divided by time.

7. What is the relationship between current and voltage in Ohm's Law?

   $V = IR$. Ohm's Law: voltage equals current times resistance.

8. What does $A$ represent in $R = \frac{\rho L}{A}$?

   Cross-sectional area of the conductor. Cross-sectional area perpendicular to current flow.

9. What does $L$ represent in $R = \frac{\rho L}{A}$?

   Length of the conductor. Physical length of the conducting material.

10. What does $t$ represent in the formula $I = \frac{Q}{t}$?

    Time in seconds. Duration over which charge flows.

11. Identify the formula for power in terms of current and voltage.

    $P = IV$. Power equals voltage times current.

12. Define conventional current direction.

    From positive to negative terminal. Convention: current flows from high to low potential.

13. If $R = 10 \, \Omega$, $V = 20 \, V$, find the current $I$.

    $I = 2 \, A$. Apply $I = \frac{V}{R} = \frac{20}{10} = 2$ A.

14. What does $Q$ represent in the formula $I = \frac{Q}{t}$?

    Charge in Coulombs. Total charge flowing through the circuit.

15. What is the unit of electrical power?

    Watt (W). Standard unit for electrical power consumption.

16. Identify the instrument used to measure electric current.

    Ammeter. Device connected in series to measure current.

17. If $\rho = 1 \Omega \cdot m$, $L = 2 \, m$, $A = 1 \, m^2$, find $R$.

    $R = 2 \, \Omega$. Apply $R = \frac{\rho L}{A} = \frac{1 \times 2}{1} = 2$ Ω.

18. If $I = 3 \, A$ and $V = 4 \, V$, find the power $P$.

    $P = 12 \, W$. Apply $P = IV = 3 \times 4 = 12$ W.

19. What is the meaning of alternating current (AC)?

    Current changes direction periodically. Current reverses direction at regular intervals.

20. If $V = 12 \, V$ and $R = 3 \, \Omega$, find the current $I$.

    $I = 4 \, A$. Apply $I = \frac{V}{R} = \frac{12}{3} = 4$ A.

21. What does $P = I^2R$ represent?

    Power formula in terms of current and resistance. Power equals current squared times resistance.

22. What is the formula for power using voltage and resistance?

    $P = \frac{V^2}{R}$. Power using voltage and resistance relationship.

23. What is the effect of increasing cross-sectional area on resistance?

    Resistance decreases. Larger area provides more paths for current.

24. Define resistivity.

    Resistance per unit length and cross-sectional area. Material property affecting electrical resistance.

25. If $I = 5 \, A$ and $V = 10 \, V$, find the resistance $R$.

    $R = 2 \, \Omega$. Apply $R = \frac{V}{I} = \frac{10}{5} = 2$ Ω.

26. What is the drift velocity of electrons?

    Average velocity of electrons due to an electric field. Slow net velocity of electrons in conductor.

27. If $V = 6 \, V$ and $R = 2 \, \Omega$, find the power $P$ using $P = \frac{V^2}{R}$.

    $P = 18 \, W$. Apply $P = \frac{V^2}{R} = \frac{36}{2} = 18$ W.

28. State the relationship between current and drift velocity.

    $I = nAve$. Current depends on carrier density, area, and velocity.

29. What is the relationship between temperature and resistivity for most conductors?

    Resistivity increases with temperature. Higher temperature increases atomic vibrations and resistance.

30. What does $\rho$ represent in $R = \frac{\rho L}{A}$?

    Resistivity. Material's inherent resistance property.

31. What is the SI unit of charge?

    Coulomb (C). Standard unit for electric charge quantity.

32. State the formula for resistance using resistivity.

    $R = \frac{\rho L}{A}$. Resistance depends on material and geometry.

33. Describe the flow of current in a conductor.

    Flow of electrons. Electrons move through conductor creating current.

34. What is the unit of resistivity?

    Ohm-meter ($\Omega \cdot m$). Unit combining resistance with length dimension.

35. What is the drift speed of electrons in a typical conductor?

    Very slow, typically mm/s. Much slower than signal propagation speed.

36. What is the value of one electron charge in Coulombs?

    $1.6 \times 10^{-19} \, C$. Fundamental charge magnitude of an electron.

37. What happens to current if resistance increases, assuming constant voltage?

    Current decreases. Ohm's Law: current inversely proportional to resistance.

38. If $I = 2 \, A$ and $R = 3 \, \Omega$, find the power $P$ using $P = I^2R$.

    $P = 12 \, W$. Apply $P = I^2R = 2^2 \times 3 = 12$ W.

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