Electrical Power and Cost Calculation Quiz

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Questions and Answers

What is the submultiple unit of power that is 1-thousandth of a watt?

Microwatt

Megawatt

Milliwatt (correct)

Kilowatt

In the context of electric power, which equation represents the relationship between work and time?

Power = work / time (correct)

Work = power / time

Power = work + time

Work = power × time

What is the unit commonly used for large amounts of electrical work or energy?

Kilowatt

Kilowatt hour (kWh) (correct)

Megawatt

Milliwatt

How is electric cost calculated for an air conditioner operating at 220 volts and 15 amperes?

$3300 \text{ watts} \times 15 \text{ amperes}$ Signup and view all the answers

What is the formula to calculate power in electric systems?

$P = V \times I$ Signup and view all the answers

What is the equivalent of 1 million watts in standard form?

$10^6$ W Signup and view all the answers

What is the resistance of a device that dissipates 1.2 kW of power when its current is 10 A?

120 $ ext{ } m{ ext{Ohm}}$ Signup and view all the answers

How much current does a 960 W coffeemaker draw from the 120 V power line?

6 A Signup and view all the answers

What is the resistance of a 20 W, 12 V halogen lamp?

72 $ ext{ } m{ ext{Ohm}}$ Signup and view all the answers

In choosing a resistor for a circuit, what is the recommended maximum power dissipation in relation to its power rating?

Never more than 50% Signup and view all the answers

In a circuit where a resistor has a 54 V IR drop and a current of 20 mA, what is the resistance of the resistor?

2.7 $ ext{ } m{ ext{kOhm}}$ Signup and view all the answers

If a circuit has a power dissipation of 100 W with a current of 5 A, what is the voltage across the circuit?

20 V Signup and view all the answers

What is the cost of using a 450-W microwave for 2 hours if the electricity rate is ₺0.08/kWh?

₺1.44 Signup and view all the answers

A 60-W light bulb is used for 5 hours per day for a month at ₺0.09/kWh. What is the total cost of using this light bulb for the month?

₺4.86 Signup and view all the answers

If a device operates at 120 W and runs for 8 hours a day at a cost of ₺0.06/kWh, what is the daily cost of operating this device?

₺6.72 Signup and view all the answers

What is the total cost of using a computer that consumes 250 W of power for 4 hours per day at a rate of ₺0.10/kWh for a month?

₺7.20 Signup and view all the answers

If a device with a power rating of 90 W runs for 6 hours a day, how much does it cost to operate it for a week at an electricity rate of ₺0.05/kWh?

₺4.32 Signup and view all the answers

A refrigerator consumes 400 W of power and runs for 24 hours a day at a rate of ₺0.12/kWh. What is the monthly cost of operating this refrigerator?

₺115.20 Signup and view all the answers

Study Notes

Electrical Power Units

Milliwatt (mW): One-thousandth of a watt (1 mW = 0.001 W)
Kilowatt (kW): One thousand watts (1 kW = 1000 W)
Megawatt (MW): One million watts (1 MW = 1,000,000 W)

Power and Work Relationship

Power (P) is the rate at which work (W) is done over time (t)
Formula: P = W / t

Electrical Work and Energy

Kilowatt-hour (kWh): A unit of energy, equivalent to the amount of energy used by a 1 kW device operating for one hour.

Electrical Cost Calculation

Cost Calculation: Cost = Power (kW) × Time (hours) × Rate (₺/kWh)
- Example: Air conditioner operating at 220 volts and 15 amperes:
  - Power (kW) = (Voltage × Current) / 1000 = (220 × 15) / 1000 = 3.3 kW
  - Cost (assuming a rate of ₺0.08/kWh) = 3.3 kW × Time (hours) × ₺0.08/kWh

Power Calculation in Electrical Systems

Formula: P = V × I
- Where:
  - P = Power (watts)
  - V = Voltage (volts)
  - I = Current (amperes)

Resistance Calculation

Formula: R = V²/P
- Where:
  - R = Resistance (ohms)
  - V = Voltage (volts)
  - P = Power (watts)

Power Dissipation in Resistors

Recommended Maximum Power Dissipation: Ideally, choose a resistor with a power rating at least twice the expected power dissipation in the circuit.

Calculating Current

Formula: I = P/V
- Where:
  - I = Current (amperes)
  - P = Power (watts)
  - V = Voltage (volts)

Electrical Cost Calculations

General Calculation: Cost = Power (kW) × Time (hours) × Rate (₺/kWh)
Example: Microwave (450 W) running for 2 hours at a rate of ₺0.08/kWh
- Cost = (450 W / 1000) × 2 hours × ₺0.08/kWh = ₺0.072
Another Example: Light bulb (60 W) used for 5 hours per day for a month (30 days) at a rate of ₺0.09/kWh
- Total Cost = (60 W / 1000) × 5 hours/day × 30 days × ₺0.09/kWh = ₺0.81
Calculating Daily Cost: Device (120 W) operating for 8 hours a day at a rate of ₺0.06/kWh
- Daily Cost = (120 W / 1000) × 8 hours × ₺0.06/kWh = ₺0.0576
Calculating Monthly Cost: Computer (250 W) used for 4 hours per day at a rate of ₺0.10/kWh for a month
- Monthly Cost = (250 W / 1000) × 4 hours/day × 30 days × ₺0.10/kWh = ₺30
Weekly Operating Cost: Device (90 W) running for 6 hours per day at a rate of ₺0.05/kWh
- Weekly Cost = (90 W / 1000) × 6 hours/day × 7 days × ₺0.05/kWh = ₺0.189
Monthly Operating Cost: Refrigerator (400 W) running 24 hours a day at a rate of ₺0.12/kWh
- Monthly Cost = (400 W / 1000) × 24 hours/day × 30 days × ₺0.12/kWh = ₺34.56

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Description

Test your knowledge on calculating electrical power, energy consumption, and cost in electrical circuits. Topics include converting watts to kilowatts, multiplying power by hours to get energy, determining the output voltage of a power supply, and calculating the cost of electricity usage.