Practice: Brightness, Switches and More Power
Level 1
1.
When any four resistors are connected in parallel, the _______ each resistor is the same.
(A) charge on (B) current through (C) power from (D) resistance of (E) voltage across
2. A certain coffeepot draws 4.0 A of current when it is operated on 120 V household lines. If electrical energy
costs 10 cents per kilowatt–hour, how much does it cost to operate the coffeepot for 2 hours?
(A) 2.4 cents (B) 4.8 cents (C) 8.0 cents (D) 9.6 cents (E) 16 cents.
Level 2
1. A circuit is connected as shown. All light bulbs are identical. When the switch in the circuit is closed
illuminating bulb #4, which other bulb(s) also become brighter?
(A) Bulb #1 only (B) Bulb #2 only (C) Bulbs #2 and #3 only (D) Bulbs #1, #2, and #3
(E) None of the bulbs.
2.
3. What is the current I1?
(A) 0.8 mA (B) 1.0 mA (C) 2.0 mA (D) 3.0 mA (E) 6.0 mA
4. How do the currents I1, I2, and 13 compare?
(A) I1 > I2 > I3 (B) I1 > I3 > I2 (C) I2 > I1 > I3 (D) I3 > I1 > I2 (E) I3 > I2 > I1
5. The circuit shown has an ideal ammeter with zero resistance and four identical resistance light bulbs which are
initially illuminated. A person removes the bulb R4 from its socket thereby permanently breaking the electrical
circuit at that point. Which statement is true of the circuit after removing the bulb?
(A) The voltage from B → C increases.
(B) The power supplied by the battery increases
(C) The voltage across R1
(D) The ammeter reading is unchanged.
increases.
(E) The bulb R2 maintains the same brightness.
Free Response Practice
2002B3B. Lightbulbs of fixed resistance 3.0 Ω and 6.0 Ω, a 9.0 V battery, and a switch S are connected as
shown in the schematic diagram above. The switch S is closed.
a. Calculate the current in bulb A.
b. Which lightbulb is brightest? Justify your answer.
c. Switch S is then opened. By checking the appropriate spaces below, indicate whether the brightness of
each lightbulb increases, decreases, or remains the same. Explain your reasoning for each lightbulb.
i. Bulb A: The brightness increases decreases remains the same
Explanation:
ii. Bulb B: The brightness increases decreases remains the same
Explanation:
iii. Bulb C: The brightness increases decreases remains the same
Explanation:
Jedi
6. Suppose you are given a constant voltage source V0 and three resistors R1, R2, and R3 with R1 > R2 > R3. If
you wish to heat water in a pail which of the following combinations of resistors will give the most rapid
heating?
7. Which of the following combinations of 4Ω resistors would dissipate 24 W when connected to a 12 Volt
battery?