An ideal black body at room temperature is thrown into a furnance.It is observed that

Answer

To solve the question about an ideal black body being thrown into a furnace, we can break down the process into clear steps:

### Step 1: Understanding the Black Body
An ideal black body is defined as a perfect absorber and emitter of electromagnetic radiation. It absorbs all incident radiation regardless of frequency or angle of incidence.

**Hint:** Remember that a black body does not reflect any light; it absorbs all incoming radiation.

### Step 2: Initial Condition
When the black body is at room temperature and is thrown into a furnace, it is initially at a lower temperature than the furnace. At this point, it will absorb the heat from the furnace.

**Hint:** Consider how temperature affects the emission and absorption of radiation.

### Step 3: Appearance of the Black Body
Since the black body absorbs all incident radiation, it will appear dark when it first enters the furnace. This is because it is not yet emitting any visible light; it is only absorbing energy.

**Hint:** Think about why objects appear dark or bright based on their absorption and emission properties.

### Step 4: Equilibrium Temperature
As the black body continues to absorb heat from the furnace, its temperature will rise. Eventually, it will reach thermal equilibrium with the furnace, meaning its temperature will equal that of the furnace.

**Hint:** What happens when two objects at different temperatures come into contact?

### Step 5: Emission of Radiation
Once the black body reaches the same temperature as the furnace, it will start to emit radiation. At this point, it will emit energy in the form of electromagnetic radiation, which can include visible light.

**Hint:** Consider how the emission of radiation changes with temperature.

### Step 6: Brightness of the Black Body
As the black body emits radiation, it will appear to glow and will be at its brightest when its temperature is equal to that of the furnace. This is due to the black body radiating energy effectively at this temperature.

**Hint:** Recall the relationship between temperature and the intensity of emitted radiation.

### Conclusion
Initially, the black body appears dark as it absorbs energy, and once it reaches the temperature of the furnace, it starts to emit radiation and appears bright.

**Final Answer:** The correct option is that the black body is initially dark and later becomes the brightest when its temperature equals that of the furnace.