Book2: Chapter6: Working with Power Flashcards
Volt
volt is a unit of electrical potential difference or the potential difference across a conductor when a current of one ampere dissipates one watt of power.
In water terminology, voltage is represented by the pressure that is the water supply tank. This is a potential because unless you provide an exit path for water to leave the tank, this potential is not realized. If you increase the pressure in the tank, you increase the potential to supply water or power.
Ohm
An ohm is a measure of resistance or electrical impedance. When comparing electricity with water, resistance is determined by the size or diameter of the hose or pipe that is used to supply water, where a smaller hose produces more resistance.
Amp
An ampere (amp) is a unit of electric current or the measure of electrical flow. When referring to water, it is also the rate of water flow. There is a direct relationship between volts, resistance, and current: If you reduce resistance or increase voltage, you increase the current. This relationship — Ohm’s Law — is represented by this formula
I = V / R
where I is current (amps), V is voltage (volts), and R is resistance (ohms).
Watt
The technical definition of a watt is that it is a unit of power, equal to one joule per second. If you equate this to water again, watts have you use flowing water to do something. If this water runs over a waterwheel, watts are the measure of how fast the wheel can be turned by the water. If you increase the current, the wheel is able to turn faster. The formula to calculate watts is
P = V * I
where P is power (watts), V is voltage (volts), and I is current (amps).
DC voltage regulation
to provide a very small tolerance of error to the devices receiving the power. Typically, a +/–5 percent voltage differential is allowed through the specification for 12VDC, 5VDC, and 3.3VDC connections.
DC voltage regulation
to provide a very small tolerance of error to the devices receiving the power. Typically, a +/–5 percent voltage differential is allowed through the specification for 12VDC, 5VDC, and 3.3VDC connections.
Over-current protection (OCP)
specifies that the power supply should handle some level of abnormally high current to prevent fuses in the power supply from blowing unnecessarily.
Power Spike
Sharp increases in line voltage caused by a problem with the power utility equipment, which may be traced back to faulty transformers or lightning strikes.
Power surges
power surges are increases in line voltage that usually last longer than a spike.
Noise
Interference caused by items not directly connected to the power system. Power lines running near fluorescent lights or microwaves can have their AC sine waves altered or chopped, which affects devices receiving their power.
Brownout
The opposite of a power surge in that the line power is below normal for a period of time ranging from seconds to minutes. If the brownout exceeds the Input-Under Voltage limits of the power supply, the power supply will shut off.
What are the main power voltages that are provided by standard computer power supplies? (Select all that apply.)
(A) 2.1V
(B) 3.3V
(C) 5V
(D) 12V
B, C, D. ATX-based power supplies provide power to devices at 3.3VDC, 5VDC, and 12VDC. See “Identifying the Purpose of Power Supply Units.”
The local city power supply for your building has degraded to a point where you regularly suffer from blackout conditions. What device will help you deal with this issue?
(A) Capacitor
(B) Surge suppressor
(C) Inline UPS
(D) Line conditioner
Inline UPS devices deal with blackout situations, while line conditioners may be able to deal with some brownout situations. Surge suppressors only deal with power surges, while capacitors are electronic devices which can store an electrical charge. Review
What items should be considered when purchasing a UPS? (Select two items.)
(A) Power consumption of protected devices
(B) Types of hard drives in protected devices
(C) Runtime of protected devices
(D) Amount of RAM in protected devices
A, C. Both the desired runtime of devices, as well as their power consumption, are required to determine the required performance characteristics of a UPS, as they will determine the size of the required battery capacity in the UPS. Check out
What are the standard input voltages for power supplies? (Select all that apply.)
(A) 110VDC
(B) 120VAC
(C) 240VDC
(D) 240VAC
B, D. 120VAC and 240VAC are the two power input voltages that are handled by power supplies. Peruse
