Bennett Mechanical Electricity and Circuits Questions and Answers 1 — Questions and Answers
Question 1: In the circuit diagram shown, three identical light bulbs are connected to a battery. If bulb B burns out (creating an open circuit), what will happen to bulbs A and C?
- Bulb A will turn off, and bulb C will remain lit. (Correct answer)
- Both bulbs A and C will turn off.
- Bulb A will get brighter, and bulb C will turn off.
- Bulb A will turn off, and bulb C will get brighter.
Correct answer: Bulb A will turn off, and bulb C will remain lit.
This is a combination series-parallel circuit. Bulbs B and C are in parallel with each other, and that parallel combination is in series with bulb A. Current flows from the battery through bulb A, then splits to go through bulbs B and C. If bulb B burns out, the path through it is opened. Current can no longer flow through B, but it can still flow through the series path of A and C. Therefore, A and C will remain lit. However, the total resistance of the circuit increases (as the parallel path is removed), causing the total current from the battery to decrease, making both A and C dimmer than before, but they remain on. The key is that the circuit for A and C remains complete.
Question 2: Which of the following best describes the primary function of a fuse in an electrical circuit?
- To store electrical energy for later use.
- To increase the voltage of the circuit.
- To protect the circuit from excessive current. (Correct answer)
- To regulate the flow of current to a constant value.
Correct answer: To protect the circuit from excessive current.
A fuse is a safety device containing a metal strip or wire that melts and breaks the circuit if the current exceeds a safe level. Its sole purpose is to provide overcurrent protection, preventing damage to the circuit's components and reducing fire risk. It does not store energy, increase voltage, or regulate current.
Question 3: Two copper wires are of the same length, but one is thicker than the other. Which statement is true regarding their electrical resistance?
- The thicker wire has less resistance. (Correct answer)
- The thinner wire has less resistance.
- Both wires have the same resistance.
- The resistance depends on the voltage applied, not the thickness.
Correct answer: The thicker wire has less resistance.
The electrical resistance of a wire is inversely proportional to its cross-sectional area. A thicker wire has a larger cross-sectional area, which provides more pathways for the electric current to flow, thus reducing the overall resistance. Think of it like a water pipe: a wider pipe allows more water to flow through with less opposition.
Question 4: In a simple series circuit, if you add another resistor, what happens to the total resistance and the total current of the circuit?
- Total resistance decreases, and total current increases.
- Total resistance increases, and total current decreases. (Correct answer)
- Total resistance increases, and total current stays the same.
- Total resistance stays the same, and total current decreases.
Correct answer: Total resistance increases, and total current decreases.
In a series circuit, resistors are connected end-to-end, creating a single path for the current. The total resistance is the sum of all individual resistances. Therefore, adding another resistor increases the total resistance. According to Ohm's Law (V=IR), if the voltage (V) from the source remains constant and the total resistance (R) increases, the total current (I) must decrease.
Question 5: A technician accidentally drops a metal wrench across the positive and negative terminals of a live car battery. This creates a dangerous situation known as a:
- Parallel circuit
- Open circuit
- Series circuit
- Short circuit (Correct answer)
Correct answer: Short circuit
A short circuit is an unintended, low-resistance path for current to flow between two points in a circuit. The metal wrench provides a very low-resistance path directly between the battery's positive and negative terminals, causing an extremely high and dangerous amount of current to flow. An open circuit is a break in the path, which would stop current flow entirely.
Question 6: According to Ohm's Law, if the voltage across a resistor is doubled, what happens to the current flowing through it?
- The current is halved.
- The current is quartered.
- The current is doubled. (Correct answer)
- The current remains the same.
Correct answer: The current is doubled.
Ohm's Law states that Voltage (V) = Current (I) × Resistance (R). This can be rearranged to I = V/R. This formula shows that current is directly proportional to voltage, assuming resistance is constant. Therefore, if you double the voltage (V), the current (I) will also double to maintain the equality.
