Formulas / Units
3.4 Calculations
3.5 Calculations
Mixed
100

Write the 3 equations you are given with Ohm's law.

V= 

I=

R=

V=IR

I=V/R

R=V/I

100

Calculate the current if a 12 V battery is connected to a 4 Ω resistor.

I = V/R = 12/4 = 3 A

100

Calculate the power of a device using 5 V and 2 A.

P = VI = 5 × 2 = 10 W

100

BC Hydro charges $0.12 per kWh. How much does it cost to run a 100 W light bulb for 10 hours?

  • 100 W = 0.1 kW
  • Energy = 0.1 × 10 = 1.0 kWh
  • Cost = 1.0 × $0.12
  • $0.12
200

What are the SI units for voltage, current, and resistance?

  • Voltage = Volt (V)
  • Current = Ampere (A)
  • Resistance = Ohm (Ω) 
200

Calculate the resistance if a circuit has a voltage of 18 V and a current of 3 A.

R = V/I = 18/3 = 6 Ω

200

Calculate the electrical power supplied to a 12V electrical heater when the current passing through it is 3.0A.

P = IV

I = 3.0A 

V = 12V

P = (3.0A)(12V) = 36W

200

An appliance costs $1.20 to run. Electricity costs $0.15/kWh. How much electrical energy did the appliance use?

  • Energy = Cost ÷ Rate
  • Energy = $1.20 ÷ $0.15
  • 8 kWh
300

What are the formula(s) for power?

P = VI

P = E/t

300

Calculate the voltage if a current of 5 A flows through a 10 Ω resistor.


V = IR = 5 × 10 = 50 V

300

A 1500 W space heater runs for 2 hours. How much energy does it use in kWh?

  • Convert watts to kilowatts: 1500 W = 1.5 kW
  • Energy = Power × Time
  • Energy = 1.5 kW × 2 h
  • 3.0 kWh
300

A 12 V battery is connected to a 2 Ω resistor and a 4 Ω resistor in series. What is the voltage drop across the 4 Ω resistor?

  • Total resistance = 6 Ω
  • Current total = 12 V ÷ 6 Ω = 2 A (also = I2)
  • Voltage drop 2 = I2R2 = 2 A × 4 Ω

8 V

400

A toaster has a resistance of 20 Ω and uses 6 A of current. What is the voltage?

V = IR = 20 × 6 = 120 V

400

A 60 W light bulb runs for 10 minutes. How much energy is used in Joules?


  • Time = 10 × 60 = 600 s
  • E = Pt
  • E = 60 × 600
  • 36 000 J
400

A 24 V battery is connected to three resistors in series. The voltage drops across the first two resistors are 5 V and 8 V. What is the voltage drop across the third resistor?

  • Total voltage = 24 V
  • Third drop = 24 − 5 − 8
  • 11 V
500

How do the formulas for V, I, and R differ between a series circuit and a parallel circuit?

Series

- Current is the same everywhere.

- Voltage is the sum of all

Parallel

  • Voltage is the same across the circuit
  • Current is the sum of all
500

A resistor has a resistance of 15 Ω and a voltage of 90 V. Find the current.

I = V/R = 90/15 = 6 A

500

An electric kettle rated at 1800 W is used for 15 minutes. 

How much energy does it use in kWh?


  • 1800 W = 1.8 kW
  • 15 min = 0.25 h
  • Energy = 1.8 × 0.25 = 0.45 kWh


500

A 2.0 kW portable heater runs for 8 hours every day for 5 days. Electricity costs $0.14/kWh. What is the total cost?

  • Energy per day = 2.0 × 8 = 16 kWh
  • Total energy = 16 × 5 = 80 kWh
  • Cost = 80 × $0.14
  • $11.20
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