Assertion : Eddy currents heat up the core and dissipate electrical energy in the form of heat.
Reason : Eddy currents are always undesirable.

Explanation

To solve the assertion-reason question, we will analyze both the assertion and the reason separately.

### Step 1: Analyze the Assertion
- **Assertion**: "Eddy currents heat up the core and dissipate electrical energy in the form of heat."
- **Explanation**: Eddy currents are loops of electrical current that are induced within conductors by a changing magnetic field due to Faraday's law of electromagnetic induction. When these currents flow through the resistance of the material, they generate heat due to Joule heating (I²R losses). Therefore, the assertion is **correct**.

### Step 2: Analyze the Reason
- **Reason**: "Eddy currents are always undesirable."
- **Explanation**: While it is true that eddy currents can lead to energy losses in many applications (like transformers), they are not always undesirable. In fact, eddy currents can be harnessed for useful applications such as:
- Electromagnetic damping (used in instruments)
- Induction heating (used in cooking and metal processing)
- Magnetic braking systems (used in trains)

Thus, the reason is **incorrect**.

### Step 3: Conclusion
- The assertion is **correct**.
- The reason is **incorrect**.
- Therefore, the answer to the assertion-reason question is that the assertion is true, but the reason is false.

### Final Answer
- Assertion: True
- Reason: False

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