What does the lumen method estimate in lighting design?
A Average illuminance
B Peak current
C Motor torque
D Cable resistance
Answer: A. Average illuminance. The lumen method estimates average illuminance from lamp lumens, number of lamps, utilization, maintenance and room area.
What does coefficient of utilization represent?
A Lamp power factor
B Room temperature rise
C Supply voltage variation
D Useful lumens reaching workplane
Answer: D. Useful lumens reaching workplane. The coefficient of utilization is the fraction of lamp lumens that effectively reaches the working plane.
What does a lighting maintenance factor account for?
A Grid frequency change
B Light loss over time
C Motor slip
D Welding current
Answer: B. Light loss over time. Maintenance factor accounts for lumen depreciation, dirt and other reductions between maintenance intervals.
What is the standard unit of average illuminance?
A Lumen
B Candela
C Kelvin
D Lux
Answer: D. Lux. Average illuminance is measured in lux, equal to lumens per square metre.
If distance from a point source doubles, normal illuminance becomes what?
A One half
B Twice
C One quarter
D Four times
Answer: C. One quarter. Inverse-square behavior gives E proportional to 1/r squared, so doubling distance reduces illuminance to one quarter.
At incidence angle ΞΈ, what factor modifies point-source illuminance?
A Sine of distance
B Square of frequency
C Cosine of angle
D Tangent of voltage
Answer: C. Cosine of angle. For an inclined receiving plane, illuminance includes a cosine factor for the angle between the light ray and surface normal.
What does an LED driver provide?
A Water flow
B Wind direction
C Mechanical torque
D Regulated current or voltage
Answer: D. Regulated current or voltage. An LED driver conditions the supply and controls current or voltage within the LED's operating limits.
Why do discharge lamps need a ballast?
A Increase room lux automatically
B Measure lamp color
C Stabilize and limit current
D Store electrical energy for months
Answer: C. Stabilize and limit current. A discharge lamp can exhibit negative differential resistance, so a ballast stabilizes and limits its current.
What is a resistance furnace commonly suited for?
A Producing grid frequency
B Measuring light output
C Controlled high-temperature heating
D Generating wind
Answer: C. Controlled high-temperature heating. Resistance furnaces use electrical heating elements to provide controlled heat for industrial processes.
How does coreless induction heating transfer energy?
A Direct contact electrodes only
B Magnetic field induces workpiece currents
C Combustion gas flow
D Visible light absorption only
Answer: B. Magnetic field induces workpiece currents. An induction coil creates an alternating magnetic field that induces eddy currents in the workpiece.
What is the heat in a resistance weld proportional to?
A Current squared times resistance
B Voltage divided by time
C Flux times speed
D Illuminance times area
Answer: A. Current squared times resistance. Joule heat is I squared R t, so current has a squared effect for fixed resistance and time.
A welding machine operates 3 minutes in a 5-minute cycle. Find duty cycle.
A 40 percent
B 50 percent
C 80 percent
D 60 percent
Answer: D. 60 percent. Duty cycle is welding time divided by total cycle time: 3 divided by 5 is 60 percent.
Why is a drooping source characteristic useful for manual arc welding?
A Raises room illuminance
B Helps stabilize welding current
C Sets turbine speed
D Eliminates electrode heating
Answer: B. Helps stabilize welding current. A drooping volt-ampere characteristic helps limit current changes as arc length varies in manual welding.
According to Faraday's law, doubling charge passed does what?
A Halves deposited mass
B Leaves mass unchanged
C Makes mass zero
D Doubles deposited mass
Answer: D. Doubles deposited mass. For the same substance and current efficiency, deposited mass is proportional to charge passed.
What occurs at the cathode in electrolysis?
A Reduction
B Oxidation
C Combustion
D Neutralization only
Answer: A. Reduction. Reduction, or electron gain, occurs at the cathode in an electrolytic cell.
What occurs at the anode in electrolysis?
A Reduction
B Oxidation
C Light emission
D Electromagnetic induction
Answer: B. Oxidation. Oxidation, or electron loss, occurs at the anode in an electrolytic cell.
During electrorefining, where do many impurities collect?
A Cathode coating only
B Insulator surface
C Anode slime
D Lamp reflector
Answer: C. Anode slime. In common copper electrorefining, less reactive impurities can settle as anode slime while copper deposits on the cathode.
What removes metal in electrochemical machining?
A Anodic dissolution
B Mechanical cutting only
C Arc melting only
D Photoelectric emission
Answer: A. Anodic dissolution. In electrochemical machining, the workpiece is the anode and material is removed by controlled anodic dissolution.
Why is a series DC motor attractive for traction?
A Fixed synchronous speed
B Zero armature current
C High starting torque
D No field winding
Answer: C. High starting torque. A series DC motor can provide high starting torque, making it useful in traction applications.
What is mechanical power at the wheels?
A Voltage divided by resistance
B Tractive force times speed
C Torque divided by flux
D Illuminance times area
Answer: B. Tractive force times speed. Mechanical power equals tractive force multiplied by vehicle speed.
What does regenerative braking require from the supply side?
A A receptive energy path
B An open circuit
C A fixed resistor only
D Zero DC-link voltage
Answer: A. A receptive energy path. The generated energy must be accepted by storage, another load or a receptive supply; otherwise braking energy needs dissipation.
What is rheostatic braking?
A Returning all energy to grid
B Increasing lamp flux
C Charging a battery only
D Dissipating generated energy in resistor
Answer: D. Dissipating generated energy in resistor. In rheostatic braking, a resistor converts generated electrical energy into heat.
What does one kilowatt-hour represent?
A One kilowatt for one hour
B One kilowatt per second
C One kilovolt times one ampere
D One joule per hour
Answer: A. One kilowatt for one hour. A kilowatt-hour is energy equal to one kilowatt of power maintained for one hour.
What does load factor compare?
A Average load to peak load
B Power factor to efficiency
C Current to voltage
D Lumens to watts
Answer: A. Average load to peak load. Load factor is average demand divided by maximum demand over the same period.
What can time-of-use tariffs encourage?
A Increasing peak demand
B Shifting demand off peak
C Reducing all metering
D Changing motor poles
Answer: B. Shifting demand off peak. Time-varying prices can encourage users to move flexible consumption to lower-demand periods.