AP Physics 1:: Dc Circuits

What is ELECTRIC CURRENT, and what is the mathematical FORMULA relating current to the amount of CHARGE that flows PAST A POINT and the TIME over which that flow occurs?

- **A)** Electric current is calculated as I = Q*t (charge multiplied by time), rather than charge divided by time
- **B)** Electric current depends only on TIME, with no actual dependence on the amount of charge that flows
- **C)** Electric current is the RATE at which electric charge flows past a given point; I = Q/t (charge divided by time), measured in AMPERES (amps), where one ampere equals one coulomb per second
- **D)** This concept has no actual mathematical relationship between electric current, charge, and time

By CONVENTION, in which DIRECTION does CONVENTIONAL CURRENT flow in a circuit, relative to the actual direction that NEGATIVELY CHARGED ELECTRONS physically move?

- **A)** Conventional current flows in the SAME direction as the actual physical electron flow, with no distinction between the two
- **B)** This concept has no actual relationship between conventional current direction and the physical direction of electron flow
- **C)** Conventional current is defined by the direction electrons move, making the two directions always identical by definition
- **D)** Conventional current is defined as flowing in the direction that POSITIVE charge would move (from the positive terminal, through the circuit, to the negative terminal) -- this is OPPOSITE to the actual physical direction that negatively charged electrons move (electrons flow from negative to positive)

What is VOLTAGE (also called ELECTRIC POTENTIAL DIFFERENCE), and what does it represent in terms of ENERGY per unit CHARGE between two points in a circuit?

- **A)** This concept has no actual relationship between voltage and the energy per unit charge between two points in a circuit
- **B)** Voltage is the electric potential ENERGY DIFFERENCE per unit CHARGE between two points; V = (energy)/(charge), measured in VOLTS, where one volt equals one joule per coulomb -- voltage represents how much energy is available to move each unit of charge between those two points
- **C)** Voltage is identical to electric current, with no actual distinction between the two quantities
- **D)** Voltage measures the TOTAL charge in a circuit, rather than energy per unit charge

What is ELECTRICAL RESISTANCE, and what does a HIGHER resistance value indicate about a material's or component's OPPOSITION to the flow of electric current?

- **A)** This concept has no actual relationship between resistance and a material's opposition to current flow
- **B)** Resistance measures only the PHYSICAL SIZE of a component, with no actual relationship to its opposition to current flow
- **C)** A higher resistance value indicates LESS opposition to current flow, the reverse of the actual meaning of resistance
- **D)** Resistance is a measure of how strongly a material or component OPPOSES (resists) the flow of electric current -- a HIGHER resistance value means MORE opposition, requiring a LARGER voltage to drive the same amount of current through it

What is OHM'S LAW, and what is its mathematical FORMULA relating VOLTAGE, CURRENT, and RESISTANCE for many common circuit components (called OHMIC materials)?

- **A)** Ohm's Law states that resistance equals voltage multiplied by current (R = V*I), rather than the correct V=IR relationship
- **B)** Ohm's Law states that V = I/R (voltage equals current divided by resistance), rather than current multiplied by resistance
- **C)** Ohm's Law states that V = I*R (voltage equals current multiplied by resistance) -- for a fixed resistance, voltage and current are DIRECTLY proportional to each other; this relationship can be rearranged to solve for any one of the three quantities given the other two
- **D)** This law has no actual mathematical relationship between voltage, current, and resistance

What is the SI (metric) UNIT for ELECTRICAL RESISTANCE, and how does this unit relate to the base units of voltage and current, based on Ohm's Law?

- **A)** The SI unit for resistance is the WATT, rather than the ohm
- **B)** Resistance is measured in AMPERES, identical to the unit for current, with no distinct unit of its own
- **C)** This concept has no actual relationship between the SI unit for resistance and the base units of voltage and current
- **D)** The OHM (symbol: Omega), which is equivalent to ONE VOLT PER AMPERE (V/A) -- directly reflecting resistance's role in Ohm's Law, R = V/I (resistance equals voltage divided by current)

What is a SERIES CIRCUIT, and what CHARACTERISTIC property does the CURRENT have at EVERY point along a series circuit (assuming a single loop with no branching)?

- **A)** This concept has no actual relationship between a series circuit's structure and the current at different points within it
- **B)** In a series circuit, current is DIFFERENT at every point, depending on which component charge has already passed through
- **C)** A series circuit requires MULTIPLE branching paths for current to flow through, contradicting the single-loop definition
- **D)** A series circuit connects components in a SINGLE loop, one after another, with NO branching paths -- the CURRENT is the SAME at every point throughout a series circuit, since charge has only ONE possible path to flow through

For RESISTORS connected in SERIES, what is the FORMULA for the TOTAL (equivalent) resistance of the combination, in terms of the individual resistances?

- **A)** R_total = R1*R2*R3*... (the individual resistances multiply together), rather than adding
- **B)** R_total = R1 + R2 + R3 + ... (the individual resistances simply ADD together) -- the total resistance of a series combination is ALWAYS GREATER than any individual resistance in the combination
- **C)** This concept has no actual mathematical relationship between individual series resistances and their total combined resistance
- **D)** R_total is always EQUAL to the SMALLEST individual resistance in a series combination, regardless of the other resistance values