A 500 cd point source is 5 m from a normal plane. Find illuminance.
A 20 lux
B 10 lux
C 25 lux
D 100 lux
Answer: A. 20 lux. For normal incidence, E equals luminous intensity divided by distance squared: 500 divided by 25 is 20 lux.
A 500 cd source is 5 m away at 60° incidence. Find illuminance.
A 10 lux
B 5 lux
C 20 lux
D 40 lux
Answer: A. 10 lux. Illuminance is I cos theta divided by r squared: 500 times 0.5 divided by 25 equals 10 lux.
Twenty 2000 lm lamps have CU 0.6 and MF 0.8 in a 120 m² room. Find average lux.
A 80 lux
B 120 lux
C 160 lux
D 240 lux
Answer: C. 160 lux. Average illuminance is N times lamp lumens times CU times MF divided by area: 20 times 2000 times 0.6 times 0.8 divided by 120 equals 160 lux.
A lamp produces 900 lm using 10 W. Find efficacy.
A 90 lm/W
B 45 lm/W
C 80 lm/W
D 100 lm/W
Answer: A. 90 lm/W. Luminous efficacy is output lumens divided by input watts: 900 divided by 10 equals 90 lm/W.
A 230 V heater has resistance 46 Ω. Find its power.
A 0.5 kW
B 2.3 kW
C 1.15 kW
D 4.6 kW
Answer: C. 1.15 kW. Power equals voltage squared divided by resistance: 230 squared divided by 46 is 1150 W.
A heater draws 10 A through 5 Ω. Find power.
A 500 W
B 50 W
C 250 W
D 1000 W
Answer: A. 500 W. Resistive power is I squared R: 10 squared times 5 is 500 W.
A 5 A current flows through 4 Ω for 10 s. Find heat.
A 200 J
B 1000 J
C 500 J
D 2000 J
Answer: B. 1000 J. Joule heat is I squared R t: 25 times 4 times 10 equals 1000 J.
If spot-welding current doubles, heat is multiplied by what factor?
A Two
B Four
C Three
D Eight
Answer: B. Four. For fixed resistance and time, welding heat is proportional to current squared, so doubling current gives four times the heat.
A welder operates 3 minutes in each 5-minute cycle. Find duty cycle.
A 60 percent
B 30 percent
C 40 percent
D 80 percent
Answer: A. 60 percent. Duty cycle is on-time divided by total cycle time: 3 divided by 5 equals 60 percent.
A 2 kW load runs for 5 hours. Find energy use.
A 2.5 kWh
B 7 kWh
C 10 kWh
D 20 kWh
Answer: C. 10 kWh. Energy equals power times time: 2 kW times 5 hours is 10 kWh.
At 0.20 currency units per kWh, what is the cost of 10 kWh?
A 0.5 units
B 2 currency units
C 1 unit
D 20 units
Answer: B. 2 currency units. Energy cost is energy use times tariff: 10 kWh times 0.20 per kWh equals 2 currency units.
For the same substance and efficiency, what does doubled electrolysis charge do?
A Halves deposited mass
B Leaves mass unchanged
C Makes mass zero
D Doubles deposited mass
Answer: D. Doubles deposited mass. Faraday's law makes deposited mass proportional to charge passed when the electrochemical equivalent and current efficiency are fixed.
A substance has Z 0.000329 g/C. At 2 A for 1 hour, find deposited mass.
A 0.59 g
B 1.18 g
C 2.37 g
D 4.74 g
Answer: C. 2.37 g. Charge is 2 A times 3600 s, or 7200 C; multiplying by 0.000329 g/C gives about 2.37 g.
A vehicle needs 20 kN tractive force at 10 m/s. Find mechanical power.
A 20 kW
B 100 kW
C 200 kW
D 400 kW
Answer: C. 200 kW. Mechanical power equals force times speed: 20,000 N times 10 m/s is 200 kW.
A traction motor supplies 300 kW at 15 m/s. Find tractive force.
A 20 kN
B 5 kN
C 15 kN
D 45 kN
Answer: A. 20 kN. Force equals power divided by speed: 300,000 W divided by 15 m/s is 20,000 N.
A traction drive takes 200 kW electrically at 80% efficiency. Find shaft output.
A 40 kW
B 160 kW
C 120 kW
D 250 kW
Answer: B. 160 kW. Mechanical output is efficiency times electrical input: 0.8 times 200 kW is 160 kW.
If induction-heating frequency increases fourfold, skin depth becomes approximately what?
A Twice as large
B Four times larger
C Half as large
D Unchanged
Answer: C. Half as large. Skin depth varies approximately as one over the square root of frequency, so four times the frequency halves the depth.
A 1000 lm lamp lights a 10 m² workplane uniformly with CU 0.5 and MF 0.8. Estimate lux.
A 20 lux
B 50 lux
C 80 lux
D 40 lux
Answer: D. 40 lux. Average illuminance is 1000 times 0.5 times 0.8 divided by 10, or 40 lux.
What does a luminaire's utilization factor account for?
A Supply frequency
B Heater resistance
C Motor slip
D Room delivery of lamp lumens
Answer: D. Room delivery of lamp lumens. Utilization accounts for how fixture distribution and room geometry deliver lamp lumens to the working plane.
A 1 kW appliance runs 30 minutes. How much energy does it use?
A 0.25 kWh
B 1 kWh
C 2 kWh
D 0.5 kWh
Answer: D. 0.5 kWh. Thirty minutes is half an hour, so 1 kW times 0.5 h is 0.5 kWh.
What happens to resistive-heater power if voltage doubles and resistance stays fixed?
A It becomes four times
B It doubles
C It halves
D It stays fixed
Answer: A. It becomes four times. With resistance fixed, P equals V squared over R, so doubling voltage quadruples power.
A lighting installation draws 4 kW for 8 hours. Find daily energy.
A 12 kWh
B 24 kWh
C 40 kWh
D 32 kWh
Answer: D. 32 kWh. Daily energy equals 4 kW times 8 h, or 32 kWh.
What does a photometric measurement weight light by?
A Motor torque
B Human visual response
C Thermal conductivity
D Electrical resistance
Answer: B. Human visual response. Photometric quantities weight radiant power by the eye's wavelength sensitivity under defined viewing conditions.
A 5 kW load operates at 0.8 power factor. Find apparent power.
A 4 kVA
B 5 kVA
C 8 kVA
D 6.25 kVA
Answer: D. 6.25 kVA. Power factor equals real power divided by apparent power, so apparent power is 5 kW divided by 0.8.
What energy conversion occurs in electric traction motoring?
A Mechanical to chemical
B Electrical to mechanical
C Light to electrical
D Heat to nuclear
Answer: B. Electrical to mechanical. During motoring, electrical energy is converted by the drive and motor into mechanical work at the wheels.