An emf can be induced in stationary coil if it is kept in

Options

A. Stationary uniform magnetic field
B. Stationary nonuniform magnetic field
C. Time varying magnetic field
D. Not possible

Answer

To solve the question "An emf can be induced in a stationary coil if it is kept in", we need to analyze the conditions under which an electromotive force (emf) can be induced in a coil according to Faraday's law of electromagnetic induction.

### Step-by-Step Solution:

1. **Understanding Faraday's Law**: Faraday's law states that an emf is induced in a coil when there is a change in magnetic flux through the coil. The induced emf (ε) is given by the formula:
\[ \epsilon = -\frac{d\Phi}{dt} \]
where \(\Phi\) is the magnetic flux.

2. **Magnetic Flux**: The magnetic flux (\(\Phi\)) through a coil is defined as:
\[ \Phi = B \cdot A \cdot \cos(\theta) \]
where \(B\) is the magnetic field strength, \(A\) is the area of the coil, and \(\theta\) is the angle between the magnetic field and the normal to the surface of the coil.

3. **Stationary Coil**: Since the coil is stationary, the area \(A\) and the angle \(\theta\) do not change. Therefore, for the stationary coil, the only way to induce an emf is if the magnetic field \(B\) changes with time.

4. **Uniform vs. Non-Uniform Magnetic Field**:
- In a **uniform magnetic field**, the strength \(B\) is constant throughout the area of the coil, which means that \(\frac{dB}{dt} = 0\). Hence, no emf is induced.
- In a **non-uniform magnetic field**, the strength \(B\) varies from one point to another. If the coil is placed in a non-uniform magnetic field, the magnetic flux through the coil can change even if the coil itself is stationary. This can lead to a change in magnetic flux and thus induce an emf.

5. **Conclusion**: Therefore, an emf can be induced in a stationary coil if it is kept in a **non-uniform magnetic field** where the magnetic field strength varies with position, allowing for a change in magnetic flux through the coil.

### Final Answer:
An emf can be induced in a stationary coil if it is kept in a **non-uniform magnetic field**.

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