Review Questions - Direct Current Circuits - SAT Physics Subject Test

SAT Physics Subject Test

Chapter 10 Direct Current Circuits

Chapter 10 Review Questions

See Chapter 17 for solutions.

1. A wire made of brass and a wire made of silver have the same length, but the diameter of the brass wire is 4 times the diameter of the silver wire. The resistivity of brass is 5 times greater than the resistivity of silver. If RB denotes the resistance of the brass wire and RS denotes the resistance of the silver wire, which of the following is true?

(A) RB = RS

(B) RB = RS

(C) RB = RS

(D) RB = RS

(E) RB = RS

2. For an ohmic conductor, doubling the voltage without changing the resistance will cause the current to

(A) decrease by a factor of 4

(B) decrease by a factor of 2

(C) remain unchanged

(D) increase by a factor of 2

(E) increase by a factor of 4

3. If a 60-watt lightbulb operates at a voltage of 120 V, what is the resistance of the bulb?

(A) 2Ω

(B) 30Ω

(C) 240Ω

(D) 720Ω

(E) 7,200Ω

4. A battery whose emf is 40 V has an internal resistance of 5 Ω. If this battery is connected to a 15 Ω resistor R, what will be the voltage drop across R ?

(A) 10 V

(B) 30 V

(C) 40 V

(D) 50 V

(E) 70 V

5. Determine the equivalent resistance between points a and b.

(A) 0.167 Ω

(B) 0.25 Ω

(C) 0.333 Ω

(D) 1.5 Ω

(E) 2.0 Ω

6. Three identical light bulbs are connected to a source of emf, as shown in the diagram above. What will happen if the middle bulb burns out?

(A) All the bulbs will go out.

(B) The light intensity of the other two bulbs will decrease (but they won”t go out).

(C) The light intensity of the other two bulbs will increase.

(D) The light intensity of the other two bulbs will remain the same.

(E) More current will be drawn from the source of emf.

7. How much energy is dissipated as heat in 20 s by a 100 Ω resistor that carries a current of 0.5 A ?

(A) 50 J

(B) 100 J

(C) 250 J

(D) 500 J

(E) 1,000 J

8. Two resistors, A and B, are in series in a circuit that carries a nonzero current. If the resistance of Resistor A is 4 times greater than the resistance of Resistor B, which of the following correctly compares the currents through these resistors (IA and IB, respectively) and the voltage drops across them (VA and VB, respectively)?

(A) IA = IB and VA = VB

(B) IA = IB and VA = 4VB

(C) IA = IB and VB = 4VA

(D) IA = 4IB and VA = 4VB

(E) IB = 4IA and VB = 4VA


electric current


drift speed



ohm Ω



direct current

electromotive force (emf)

joule heat






terminal voltage

internal resistance






· Electric current is created when a potential difference (an electric field) set up between the ends of a piece of wire cause the electrons in the wire to drift through the wire with a net movement of charge.

· Resistance differs from material to material. A conductive material offers less resistance to the flow of electrons. Resistance is represented by the equation R = . If the current is large, the resistance is low; if the current is small, resistance is high.

· Electric circuits are paths along which electrical energy is released (as from a battery or other source of electrical energy). Electrical energy can only be released when the current has a complete conducting path available from one side of the potential difference to the other.

· Power is the rate at which energy is released. Use the formula P = IV. This equation is relevant for the power delivered by the battery to a circuit as well as for resistors. Resistors dissipate energy as heat.

· Circuit analysis is a way to specify the current, voltage, and power associated with each element in a circuit (batteries, resistors, and connecting wires).

· Combinations of resistors occur in a series (one after the other) or in parallel (side-by-side).

· Resistance–Capacitance (RC) circuits are simple circuits for charging a capacitor. An RC circuit consists of a battery which holds the potential energy that will charge the capacitor, a switch that closes the circuit and allows the current to flow, as well as a resistor that will use the energy to produce heat.