4.2.2 Electric current (3)
Resources |
Revision Questions |
Physics
Login to see all questions
Click on a question to view the answer
1.
A current of 2 Amperes flows through a wire in 5 seconds. Calculate the total charge that passes a point in the wire during this time. Show your working.
Given:
- Current (I) = 2 Amperes
- Time (t) = 5 seconds
Formula: I = Q / t can be rearranged to solve for Q: Q = I * t
Calculation:
Q = 2 A * 5 s = 10 Coulombs
Answer: The total charge that passes a point in the wire during this time is 10 Coulombs.
2.
A student is investigating the properties of direct and alternating current. They connect a light bulb to a d.c. power supply and a different light bulb to an a.c. power supply. Explain, in terms of the behaviour of the electrons, why the light bulb connected to the a.c. power supply appears brighter than the light bulb connected to the d.c. power supply, assuming both bulbs are designed to operate at the same voltage.
The light bulb connected to the a.c. power supply appears brighter because the electrons in the light bulb are being repeatedly pushed and pulled by the changing direction of the current. This repeated movement causes the filament in the light bulb to heat up more rapidly and to a higher temperature.
In a d.c. circuit, the electrons flow in a constant direction, resulting in a more steady heating of the filament. While the voltage is the same, the alternating nature of the current in the a.c. circuit means the filament is being heated more frequently, leading to a higher overall brightness. Essentially, the a.c. current is delivering energy to the filament more effectively due to the repeated changes in direction.
3.
Explain the difference between conventional current and electron flow. Include a statement about which direction is conventionally used in circuit diagrams and why this convention is maintained.
Conventional current is defined as the flow of positive charge. Electron flow is the actual movement of electrons, which are negatively charged. Therefore, electron flow is from negative to positive, while conventional current is from positive to negative.
Circuit diagrams conventionally show current flowing from the positive terminal to the negative terminal. This convention is maintained for historical reasons, dating back to the early days of electrical circuits, before the discovery of electrons. It simplifies circuit analysis and allows engineers to easily trace the flow of current without needing to constantly consider the sign of the charge carriers. While it's important to remember the actual electron flow direction, using the conventional current direction simplifies circuit design and understanding.