Number of kilowatt-hours = `("volt " xx "ampere" xx "______")/( 1000)`

Options

A. time in seconds
B. time in minutes
C. time in hours
D. time in days

Answer

To solve the question regarding the formula for calculating the number of kilowatt-hours, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Kilowatt-Hour**:
- A kilowatt-hour (kWh) is a unit of energy that represents the amount of energy consumed or produced over one hour at a rate of one kilowatt.

2. **Identify the Formula for Power**:
- The power (P) in watts can be calculated using the formula:
\[ P = V \times I \]
where \( V \) is the voltage in volts and \( I \) is the current in amperes.

3. **Convert Power to Kilowatts**:
- Since 1 kilowatt (kW) is equal to 1000 watts (W), we can express power in kilowatts as:
\[ P \text{ (in kW)} = \frac{V \times I}{1000} \]

4. **Relate Power to Energy**:
- The energy (E) in kilowatt-hours is calculated by multiplying power in kilowatts by time in hours:
\[ E \text{ (in kWh)} = P \text{ (in kW)} \times \text{Time (in hours)} \]

5. **Substituting Power into the Energy Equation**:
- Replacing \( P \) in the energy equation with the expression we derived:
\[ E = \left(\frac{V \times I}{1000}\right) \times \text{Time (in hours)} \]

6. **Finalizing the Equation**:
- Rearranging gives us:
\[ \text{Number of kilowatt-hours} = \frac{V \times I \times \text{Time (in hours)}}{1000} \]

7. **Identifying the Missing Unit**:
- From the equation, it is clear that the missing unit in the question is **Time in hours**.

### Final Answer:
The missing unit is **Time in hours**.