955 Exam Answered

955 Exam Answered State Ohm's law - Answer- V=IXR R=V/I I=V/R If current goes down, what does resistance do? - Answer- Reistance goes up If Voltage is CONSTANT and Resistance goes DOWN, what must Current do? - Answer- Current HAS to go UP! What is the definition of a short circuit? - Answer- Zero resistance. Circuit has high current, and zero resistance. What would cause Current to DECREASE in a circuit, IF Voltage remained CONSTANT? - Answer- INCREASSE in Resistance What is a Transformer? - Answer- An electrical device that transfers energy from one electrical circuit to another by magnetic coupling, aka: Mutal Induction. One set of windings induce a voltage in the other set of windings. What are Transformers used for? - Answer- Used to convert between high and low voltages and for impedance transformation. State the Power formula. - Answer- P = V X I power equals voltage times current What are air core transformers main use? - Answer- Radio frequency circuits ABOVE 20kHz What are iron core transformers main use? - Answer- Lower frequency: below 20kHz To transmit electrical power what must a transformer have? - Answer- Has a very high current OR very high voltage. High current means a high flow rate of electrons. This requires a VERY large COPPER or ALUMINUM cable. *How does a Power Station function? - Answer- Uses high voltage to reduce the amount and weight and therefore What is the symbol for a transformer? - Answer- XX What kind of electrical charge does a neutron have? - Answer- Neutral What kind of electrical charge does a proton have? - Answer- Positive The step down transformer outside a house does what? - Answer- Reduces the voltage to a usable voltage for the house ELECTRIC, which are usually TWO 120VAC legs. What is an electronic shunt? - Answer- A device which allows electric current to pass around a point in a circuit. A shunt as CIRCUIT PROTECTION: is a device that is commonly called a CROWBAR circuit and is used when a circuit must be protected from over VOLTAGE. What does a capacitor do? - Answer- When used as a shunt, redirects hight frequency nouse to ground before it can transmit to the load or other circuit components. This is why they are used so frequently in DC power supplies as AC filters. What is a Zenner Diode? - Answer- Voltage Regulator used when devices are sensitive to reverse polarity in a signal to protect a circuit. Also used in a power supply to cause a fuse or other current limiting circuit to open. How does a shunt used as Circuit Protection work? - Answer- When a shunt detects an over VOLTAGE it causes a short circuit between the power supply and its return lilne, which produces an immediate drop in voltage and a resultant HIGH CURRENT which opens the CURRENT SENSITIVE DEVICE in the circuit usall a FUSE or CIRCUIT BREAKER. What is ESD? - Answer- ELECTROSTATIC DISCHARGE: a brief an abrupt electric current that flows between two objects at DIFFERENT ELECTRICAL POTENTIALS which is caused by CONTACT, or INDUCED by AN ELECTROSTATIC field. What is a RESISTOR? - Answer- Electronical device that RESISTS the FLOW of ELECTRICAL CURRENT. Symbol for: ZENNER DIODE - Answer- x Definition of Zener Diode: - Answer- Voltage Regulator, typically REVERSED BIASED. If reverse voltage of a circuit is INCREASED the zener begins to LEAK current until the breakdown voltage is where the current INCREASES DRAMATICALLY. Zener diode will CONDUCT to keep the voltage REGULATED. What is LED - Answer- Light Emitting Diode emits different colors and are made of different semi-conductor materials, and require different energies to light them. The FLAT side of the LED is the NEGATIVE terminal and the LONGER LEG is the POSITIVE lead. What is a DIODE? - Answer- Conducts electric current very EASILY in one direction and VERY POORLY in the other direction. Allows DC to pass. IF it is FORWARD BIASED it CONDUCTS with a .7VDC drop across it if it is made of SILILCON. .3V if made of GERMANIUM. Also known as a RECTIVIER because it will stop the flow of AC