Electric Current - AP Physics 2

1. What is the unit of electrical power?

   Watt (W). Rate of energy transfer or consumption.

2. Convert 1 milliampere to amperes.

   $1 \text{ mA} = 0.001 \text{ A}$. Milli prefix means one thousandth.

3. State the formula for calculating resistance using resistivity.

   $R = \frac{\rho L}{A}$. Resistance depends on material, length, and cross-sectional area.

4. What is the definition of resistivity?

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

5. What is the unit of resistance?

   Ohm ($\text{Ω}$). Named after Georg Ohm, symbol omega.

6. What is the effect of adding resistors in parallel on total resistance?

   Total resistance decreases. Parallel paths reduce overall resistance.

7. What is the effect of temperature on resistance in conductors?

   Resistance increases. Higher temperature increases atomic vibrations.

8. What is the formula for electrical power in terms of current and voltage?

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

9. Calculate the potential difference if $I = 1.5 \text{ A}$ and $R = 6 \text{ Ω}$.

   $V = 9 \text{ V}$. Apply $V = IR = 1.5 \times 6 = 9$ V.

10. What does an ohmmeter measure?

    Resistance. Instrument for measuring electrical resistance.

11. How is current measured?

    Using an ammeter. Ammeter connected in series with circuit.

12. Calculate the energy used if $P = 100 \text{ W}$ and $t = 2 \text{ hours}$.

    $E = 200 \text{ Wh}$. Apply $E = Pt = 100 \times 2 = 200$ Wh.

13. What is the formula for voltage in terms of work and charge?

    $V = \frac{W}{q}$. Voltage is work per unit charge.

14. Calculate the current if $V = 12 \text{ V}$ and $R = 4 \text{ Ω}$. Use Ohm's Law.

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

15. Calculate resistance if $V = 10 \text{ V}$ and $I = 2 \text{ A}$. Use Ohm's Law.

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

16. State Ohm's Law formula.

    $V = IR$. Voltage equals current times resistance.

17. What is the formula for electric current in terms of charge and time?

    $I = \frac{q}{t}$. Current is charge divided by time.

18. What is the unit of resistivity?

    $\text{Ωm}$ (Ohm meter). Resistance times meters per square meter.

19. What is the effect of adding resistors in series on total resistance?

    Total resistance increases. Resistors in series add directly.

20. What is Kirchhoff's Junction Rule?

    Sum of currents entering = sum leaving. Conservation of charge at circuit junctions.

21. Describe the motion of electrons in a conductor.

    Drift towards positive terminal. Electrons move opposite to conventional current direction.

22. What is the formula for total resistance in parallel?

    $\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \\dots$. Reciprocals of resistances add in parallel circuits.

23. What is the effect of increasing voltage on current, assuming constant resistance?

    Current increases. Direct proportional relationship from Ohm's Law.

24. Express 5 kilowatts in watts.

    $5 \text{ kW} = 5000 \text{ W}$. Kilo prefix means one thousand.

25. What is the unit for electric charge?

    Coulomb (C). Amount of electric charge, named after Coulomb.

26. Define electric current.

    Flow of electric charge. Rate of charge flow through a conductor.

27. Calculate the power if $I = 2 \text{ A}$ and $R = 3 \text{ Ω}$. Use $P = I^2R$.

    $P = 12 \text{ W}$. Apply $P = I^2R = 2^2 \times 3 = 12$ W.

28. What is the effect of increasing resistance on current?

    Current decreases. Inverse relationship from Ohm's Law.

29. Identify the direction of conventional current flow.

    From positive to negative terminal. Conventional current flows opposite to electron flow.

30. What is the relationship between power, current, and resistance?

    $P = I^2R$. Power dissipated as heat in resistive circuits.

31. What is the formula for total resistance in series?

    $R_{total} = R_1 + R_2 + \\dots$. Individual resistances add in series circuits.

32. Calculate the total resistance for $R_1 = 5 \text{ Ω}$ and $R_2 = 10 \text{ Ω}$ in parallel.

    $R_{total} = 3.33 \text{ Ω}$. Apply $\frac{1}{R_{total}} = \frac{1}{5} + \frac{1}{10} = \frac{3}{10}$, so $R_{total} = 3.33$ Ω.

33. What is the power formula using voltage and resistance?

    $P = \frac{V^2}{R}$. Alternative power formula using voltage and resistance.

34. What is the SI unit for electric current?

    Ampere (A). Standard unit defined as one coulomb per second.

35. State the formula for electrical energy in terms of power and time.

    $E = Pt$. Energy equals power multiplied by time.

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