This set of Analog Circuits online quiz focuses on “Heat Sink for Power Transistor-2”.
1. Which of the following heat sink is used for low power application?
a) Stamped heat sink
b) Machining heat sink
c) Aluminum heat sink
d) Bolded-Fin heat sink
Explanation: Stamped heat sinks are made of metal that are stamped to form a particular shape. These are cheaper compared to extruded heat sinks. These are used for low-power applications and hence these are low in performance.
2. The performance of heat sink does not depend upon ___________
a) Choice of material
b) Protrusion design
c) Surface treatment
d) none of the mentioned
Explanation: The performance of the heat sink depends on the factors like the choice of material, protrusion design, surface treatment and air velocity. The material is preferred to have high conductivity and heat absorption. The shape and design also effect heat flow as well as coolant flow in the sink.
3. What is a heat spreader?
a) An older version of a heat sink
b) Another name for heat sink
c) Device to transfer heat from device to the sink
d) A connector for coolant to flow
Explanation: A heat spreader conducts heat between a heat source and a heat sink. Most commonly, a block of material with high thermal conductivity is used as a heat spreader.
4. Heat dissipation from heat sink take place primarily by ___________
d) All of the mentioned
Explanation: Heat dissipation from heat sink take place primarily by convection since there is no actual contact between heat sink and transistor. Heat dissipation also takes place by Radiation but it is comparatively low.
5. Heat sinks are provided with peripheral fins to ___________
a) Provide good appearance
b) Increase heat absorption
c) Increase surface area of heat dissipation
d) Provide material stability
Explanation: Heat sinks are provided with peripheral fins to increase surface area of heat conduction. Increase in dissipation also increase absorption but more correct option is c.
6. Heat sinks are usually provided with black anodized finish to ___________
a) Enhance heat dissipation by radiation
b) Enhance heat dissipation by convection
c) Prevent electrical connection
d) Remove dust accumulation
Explanation: Heat sinks are usually provided with black anodized finish to enhance heat dissipation by radiation. Anodizing thickens and toughens the naturally occurring protective oxide layer on the metal surface. It provides dielectric isolation between cooling components and the electronics in the device.
7. Which substance is used to maintain electrical insulation between a heat sink and transistor?
Explanation: Many transistors have metal cases which are connected to a lead and thus it becomes necessary to insulate the heat sink from the transistor. Insulating kits of a mica sheet and a plastic sleeve are used.
8. De-rating factor is usually expressed in ___________
Explanation: De-rating factors for determining the power dissipation rating is usually given at any temperature above 25°C. The de-rating factor is specified in W/°C.
9. Cavities embedded in heat source is also known as ___________
a) Low sink
b) Sink hole
d) Inverted sink
Explanation: Cavities embedded in heat source is also known as an inverted sink.
10. By dividing volumetric thermal resistance by required thermal resistance we will obtain ___________
a) Power dissipation of heat sink
b) Volume of heat sink
c) Maximum temperature of heat sink
d) Volume of surrounding air
Explanation: By dividing volumetric thermal resistance by required thermal resistance we will obtain volume of heat sink.
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