Watt's Law | Engineering Calculator API

Watt's Law API

Compute electrical power, current, voltage, resistance, or energy over time using Watt's Law. This endpoint is ideal for students, engineers, and developers working on circuit calculations, energy analysis, or efficiency estimations.

Law

$P = V \cdot I$

Combined with Ohm's Law:

$P = I^2 \cdot R$

$P = \frac{V^2}{R}$

Energy over time:

$E = P \cdot \Delta t$

Optional efficiency factor:

$P_{\text{out}} = \eta \cdot P_{\text{in}}$

Request Body

1{
2  "law": "watts",
3  "vars": {
4    "P": null,
5    "P_i": null,
6    "P_f": null,
7    "V": null,
8    "V_i": null,
9    "V_f": null,
10    "I": null,
11    "I_i": null,
12    "I_f": null,
13    "R": null,
14    "t": null,
15    "t_i": null,
16    "t_f": null,
17    "efficiency": 1.0
18  }
19}

Variables

Behavior Notes

• Computes missing $P$, $V$, $I$, $R$, or energy $E = P \cdot \Delta t$.

• Supports initial and final values for voltage, current, and power; automatically computes deltas.

• If $R$ is provided, voltage and current can be derived via Ohm's Law.

• Optional efficiency factor modifies power: $P_out=\eta \cdot P_in$.

• If all values are provided, the API verifies consistency.

• Division by zero (e.g. $I=0$ or $V=0$ when solving) raises an error.

Example Requests

Calculate power

1{
2  "law": "watts",
3  "vars": {
4    "V": 12,
5    "I": 2
6  }
7}

Solve for current

1{
2  "law": "watts",
3  "vars": {
4    "P": 60,
5    "V": 120
6  }
7}

Power at two voltages (same resistance)

1{
2  "law": "watts",
3  "vars": {
4    "V_i": 100,
5    "V_f": 200,
6    "R": 50
7  }
8}

Power with efficiency

1{
2  "law": "watts",
3  "vars": {
4    "V": 240,
5    "I": 10,
6    "efficiency": 0.85
7  }
8}

Example Response

1{
2  "solved": "P",
3  "value": 2040,
4  "summary": "P = V·I ·η = 2040 W  |  E = 7344000 J",
5  "inputs": {
6    "P": 2040,
7    "V": 240,
8    "I": 10,
9    "R": 24,
10    "P_i": null,
11    "P_f": null,
12    "V_i": null,
13    "V_f": null,
14    "I_i": null,
15    "I_f": null,
16    "delta_t": 3600,
17    "t_i": 0,
18    "t_f": 3600,
19    "efficiency": 0.85
20  },
21  "derived": {
22    "energy_J": 7344000,
23    "energy_kWh": 2.04,
24    "R_derived": 24,
25    "P_input": 2400,
26    "P_loss": 360
27  }
28}

Use Cases

• Electrical power calculations

• Circuit analysis and design

• Energy consumption over time

• Efficiency evaluation in power systems

• Engineering, physics, and electronics education