Analog Circuits Multiple Choice Questions on “Heat Sink for Power Transistor-1”.
1. What is the purpose of heat sink in transistor circuit?
A. Provide sufficient heat for transistor
B. Absorb excess heat from transistor
C. Keep transistor at desired temperature range
D. All of the mentioned
Answer: D
Clarification: Heat sink in a transistor circuit performs a major function of keeping temperature of transistor at a desired range and also absorbs excess heat. Self heating occurs in a transistor due to power dissipated at the collector junction. This can cause junction temperature to rise and further increases collector current, and such a process may damage the device.
2. What is the major principle behind heat sink action?
A. Avogadro’s law
B. Fourier’s law
C. Archimedes principal
D. Faraday’s law
Answer: B
Clarification: Major principle behind heat sink is Fourier’s law. Fourier’s law of heat conduction, simplified to a one-dimensional form is, when there is a temperature gradient heat will be transferred from the higher temperature region to the lower temperature region. The rate at which heat is transferred by conduction is proportional to the product of the temperature gradient and the cross-sectional area through which heat is transferred.
3. Comparing high heat objects with cooling objects which one will have slow-moving molecules?
A. High heat objects
B. Cooling objects
C. Both of them have equal molecular movement
D. Cannot be predicted
Answer: B
Clarification: Since temperature is low for cooling objects the energy of molecule will also be low.
4. If water is used as a cooling medium then it is termed as _______________
A. liquid plate
B. aqua plate
C. hot plate
D. cold plate
Answer: D
Clarification: heat sink transfers thermal energy from a high-temperature medium to a low-temperature medium like air, water etc. Usually air is used as a low-temperature medium. If water is used as medium, then it is termed as cold plate.
5. Active heat sinks are also called as ___________
A. fans
B. on sinks
C. high sinks
D. normal sinks
Answer: a
Clarification: Active heat sinks are also called as fans. Fans can be classified into ball bearing type and sleeve bearing type.
6. Passive heat sinks are made of ________________
A. Copper
B. Aluminum
C. Iron
D. Zinc
Answer: B
Clarification: The thermal conductivity of aluminum is about 235 W/mK; it is the cheapest and lightweight metal. Aluminum heat sinks are also called extruded heat sinks because they can be made using the extrusion technique.
7. Difference between the active heat sink and passive heat sink is that passive heat sink?
A. Possess mechanical components
B. Possess electrical components
C. Do not possess mechanical components
D. Do not possess metal components
Answer: C
Clarification: Unlike active heat sink passive heat sink do not possess any mechanical component and are made of aluminum finned radiator. Thus these passive heat sinks are cheaper than the active ones and only use convection to dissipate thermal energy. They are more reliable since they have no moving parts but the performance of active sinks is better in dissipating heat.
8. Which of the following heat sink is more durable?
A. Stamped heat sink
B. Ball bearing type heat sink
C. Sleeve bearing type heat sink
D. Aluminum heat sink