Electrical Circuits Quiz

What does Kirchhoff's first law state?

• The sum of the currents entering a junction equals the sum leaving.

• The total resistance in a series circuit is the sum of individual resistances.

• The total voltage in a circuit is constant.

• The power in a circuit is equal to the product of voltage and current.

Answer explanation

Kirchhoff's first law, also known as the current law, states that the total current entering a junction must equal the total current leaving it, ensuring conservation of charge in electrical circuits.

What is the formula for calculating resistance?

• R = I + V

• R = V*I

• R = I/V

• R = V/I

Answer explanation

The correct formula for calculating resistance (R) is R = V/I, where V is voltage and I is current. This relationship is derived from Ohm's Law, which states that resistance is the ratio of voltage to current.

In a series circuit, how is the total resistance calculated?

• R_total = R1 / R2 / R3

• R_total = R1 + R2 + R3 + ...

• R_total = R1 - R2 - R3

• R_total = R1 * R2 * R3

Answer explanation

In a series circuit, the total resistance is calculated by adding the individual resistances together: R_total = R1 + R2 + R3 + ... This is because the current has only one path to follow, so all resistances contribute to the total.

What is the power formula for a resistor in a circuit?

• P = IV

• P = I + V

• P = V - I

• P = V/I

Answer explanation

The power formula for a resistor is given by P = IV, where P is power, I is current, and V is voltage. This formula shows that power is the product of current and voltage, making it the correct choice.

What happens to the total resistance in a parallel circuit as more resistors are added?

• It remains the same.

• It increases.

• It doubles.

• It decreases.

Answer explanation

In a parallel circuit, adding more resistors provides additional paths for current to flow. This reduces the total resistance, as the overall effect is that the current can divide among more pathways, leading to a decrease in total resistance.

What is the unit of voltage?

• Amperes

• Volts

• Ohms

• Watts

Answer explanation

The unit of voltage is volts, which measures the electric potential difference. Amperes measure current, ohms measure resistance, and watts measure power. Therefore, the correct answer is volts.

What does internal resistance represent?

• Resistance of the circuit components.

• Resistance due to temperature changes.

• Resistance of the cell's materials.

• Resistance of the external circuit.

Answer explanation

Internal resistance refers to the resistance within the cell's materials that affects its ability to deliver current. It is not related to external circuit components or temperature changes.

What is the relationship between electromotive force (emf) and potential difference (pd) in a circuit with internal resistance?

• E = V * Ir

• E = V + Ir

• E = V / Ir

• E = V - Ir

Answer explanation

In a circuit with internal resistance, the electromotive force (emf) is equal to the potential difference (pd) plus the product of the current (I) and internal resistance (r). Thus, E = V + Ir is the correct relationship.

In a potential divider circuit, how is the output voltage across a resistor calculated?

• V = R_total / R * V_in

• V = V_in / R

• V = R / R_total * V_in

• V = I * R

Answer explanation

In a potential divider, the output voltage across a resistor is calculated using the formula V = (R / R_total) * V_in, where R is the resistance of the resistor, R_total is the total resistance, and V_in is the input voltage.

What is the purpose of a thermistor in a circuit?

• To measure current.

• To control temperature.

• To increase voltage.

• To decrease resistance.

Answer explanation

A thermistor is a type of resistor whose resistance varies significantly with temperature. Its primary purpose in a circuit is to control temperature, making it essential for temperature sensing and regulation.