# list of physics formulas class 11 chapter Transmission of Heat

## Class - 11 Chapter Transmission of Heat

### Coefficient of Thermal conductivity:

In steady state the quantity of heat Q flowing through a metal rod of length l and cross-section A in a time. t when its ends are at temperature θ1, and θ2  (θ1, θ₂) is given by

where K is coefficient of thermal conductivity

• K depends on the nature of the metal.
• It is defined as the rate of flow of heat per unit area and per unit temperature gradient in steady state.
• If one end of a metal rod is kept in a steam jacket and other end is kept in an ice block, then the amount of ice that melts is

### Junction temperature

In steady state when conduction takes place through two layers of composite wall with different thermal conductivities, then

### Thermal Resistance R

Thermal resistance R of a conductor of length l, cross-section A and conductivity K is given by

R = 1/KA

### Effective conductivity:

• Series combination: If two rods of same cross-sectional area having lengths l1 and l2 and conductivities K1 and K2 are connected in series, then in steady state conductivity of the combination K is given by

• Parallel combination: If two rods of same length having cross sectional area A1, A2 and conductivities K1, K2 are arranged in parallel, then in steady state, the conductivity of the combination is

### Emissive Power:

• The amount of energy emitted per second per unit surface area of a body at a given temperature for a given wave –length range (λ and λ + dλ) is called emissive power.
• At a given temperature if the radiations emitted have a wave length difference dλ, then the emissive power is equal to eλdλ.
• S.I unit of emissive power is Wm–2 and its dimensional formula is MT–3.

### Emissivity(e):

The ratio of radiant energy emitted by a surface to radiant energy emitted by a black body under same conditions is called emissivity. For a perfect black body emissivity e = 1

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Download the Pdf of class 11 physics formula sheet of chapter Transmission of Heat from the link given below