IB MYP 4-5 Physics- Electrical energy and power- Study Notes - New Syllabus
IB MYP 4-5 Physics-Electrical energy and power- Study Notes
Key Concepts
- Electrical energy and power
Electrical Energy and Power
Electrical Energy and Power
Electrical Energy
Electrical energy is the work done by an electric current when it flows through a component or circuit.
Formula: \( E = V \times I \times t \)
- \( E \) = electrical energy (Joules, J)
- \( V \) = potential difference (Volts, V)
- \( I \) = current (Amperes, A)
- \( t \) = time (seconds, s)
Electrical Power
Electrical power is the rate at which electrical energy is converted into other forms (heat, light, motion, etc.).
Formula: \( P = \dfrac{E}{t} \)
Since \( E = VIt \), then \( P = VI \)
Alternative Forms of Power Formula
Using Ohm’s law \( V = IR \):
\( P = VI = I^2R \)
Or in terms of voltage and resistance:
\( P = \dfrac{V^2}{R} \)
Key Notes
- High power means energy is transferred quickly.
- In real life, electrical power is measured in watts (W), where \( 1 \, \text{W} = 1 \, \text{J/s} \).
- For household electricity, energy is often measured in kilowatt-hour (kWh).
\( 1 \, \text{kWh} = 1000 \, \text{W} \times 3600 \, \text{s} = 3.6 \times 10^6 \, \text{J} \)
Example:
An electric kettle is rated at 2000 W and connected to a 230 V supply. Calculate the current drawn by the kettle.
▶️ Answer/Explanation
Step 1: Use the formula \( P = VI \).
Step 2: Rearrange to find current: \( I = \dfrac{P}{V} \).
\( I = \dfrac{2000}{230} \approx 8.7 \, \text{A} \)
Final Answer: The kettle draws \(\boxed{8.7 \, \text{A}}\).
Example:
A 100 W light bulb is switched on for 5 hours. Calculate the electrical energy consumed in kWh.
▶️ Answer/Explanation
Step 1: Convert power to kW: \( 100 \, \text{W} = 0.1 \, \text{kW} \).
Step 2: Energy in kWh = Power (kW) × Time (h).
\( E = 0.1 \times 5 = 0.5 \, \text{kWh} \)
Step 3: Convert to joules if needed: \( 0.5 \times 3.6 \times 10^6 = 1.8 \times 10^6 \, \text{J} \).
Final Answer: Energy consumed = \(\boxed{0.5 \, \text{kWh} \, (1.8 \times 10^6 \, J)}\).
Example:
A television rated at 150 W is used for 4 hours per day. How much energy does it consume in a week, and what will be the cost if 1 kWh costs $0.20?
▶️ Answer/Explanation
Step 1: Power = 150 W = 0.15 kW.
Step 2: Daily energy use = \( 0.15 \times 4 = 0.6 \, \text{kWh} \).
Step 3: Weekly energy use = \( 0.6 \times 7 = 4.2 \, \text{kWh} \).
Step 4: Cost = \( 4.2 \times 0.20 = 0.84 \, \text{USD} \).
Final Answer: The TV consumes \(\boxed{4.2 \, \text{kWh}}\) per week, costing \(\boxed{0.84 \, \text{USD}}\).