### Perfectly Black Body

• Define radiation mode of heat transfer.

• Define absorptivity, reflectivity, transmissivity, black Body, grey body, opaque body.

• Relations between emissivity and absorptivity.

### Solved Example:

#### 82-1-01

All radiations in a perfectly black body are:

### Solved Example:

#### 82-1-02

The amount of radiation mainly depends on:

### Solved Example:

#### 82-1-03

A perfect black body is one which:

### Solved Example:

#### 82-1-04

A grey body is one whose absorptivity: (ISRO RAC 2014)

### Solved Example:

#### 82-1-05

Depending on the radiating properties, a body will be considered perfectly black when:

Solution:
$\alpha$ = absorptivity, $\rho$ = reflectivity, $\tau$ = transmissivity.

### Solved Example:

#### 82-1-06

Coefficient of transmission and coefficient of reflection for a given body are 0.22 and 0.74 respectively. Then, at a given temperature, the coefficient of emission for the body is:

Solution:
Reflectivity ($\rho$) + Absorptivity ($\alpha$) + Transmissivity ($\tau$)= 1

### Solved Example:

#### 82-1-07

The coefficient of absorption of a perfectly black body is: