The cathode of a diode valve is replaced by another cathode of double the surface area. Keeping the voltage and temperature conditions the same, will the plate current decrease, increase or remain the same?

Three identical lamps each having a resistance R are connected to the battery of emf as shown in the figure. Suddenly the switch S is closed. (a) Calculate the current in the circuit when S is open and closed (b) What happens to the intensities of the bulbs A,B and C. (c ) Calculate the voltage across the three bulbs when S is open and closed (d) Calculate the power delivered to the circuit when S is opened and closed (e ) Does the power delivered to the circuit decreases, increases or remain same?

The constant A in the Richardson-Dushman equation for tungsten is 60 xx 10^(4) A m^(-2) . The work function of tungsten is 4.5 eV . A tungsten cathode having a surface area 2.0 xx 10^(-5) m^2 is heated by a 24 W electric heater. In steady state, the heat radiated by the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan constant = 6 xx 10^(-8) W m^(-2) K^(-4) . Assume that the thermions take only a small fraction of the heat supplied.

Read the following paragraph carefully and answer the following question . If the heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy . The change in temperature continues till the temperatures of both the the object attain the same value . In the process, the cold object gains heat energy and the hot objet lose heat energy . If the system of both the object is isolated from the environment by keeping it inside a heat resistance box ( meaning that the energy exchange takes place between the two object only), then no energy can flow from inside the box or come into the box. Heat is transferred from where to where ?

Read the following paragraph carefully and answer the following question . If the heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy . The change in temperature continues till the temperatures of both the the object attain the same value . In the process, the cold object gains heat energy and the hot object lose heat energy . If the system of both the object is isolated from the environment by keeping it inside a heat resistance box ( meaning that the energy exchange takes place between the two object only), then no energy can flow from inside the box or come into the box. How will you state the principle briefly ?

Read the following paragraph carefully and answer the following question . If the heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy . The change in temperature continues till the temperatures of both the the object attain the same value . In the process, the cold object gains heat energy and the hot objet losec heat energy . If the system of both the object is isolated from the environment by keeping it inside a heat resistance box ( meaning that the energy exchange takes place between the two object only), then no energy can flow form inside the box or come into the box. Which property of the substance measured using principle of heat exchange?.

Read the following paragraph carefully and answer the following question . If the heat is exchanged between a hot and cold object,the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy . The change in temperature continues till the tempertaures of both the object attain the same value . In the process, the cold object gains heat energy and the hot object lose heat energy . If the system of both the object is isolated form the environment by keeping it inside a heat resistance box ( meaning that the energy exchange takes place between the two object only), then no energy can flow from inside the box or come into the box. Which principle do we learn about from this process ?

A Tungsten cathode and a thoriated-tungsten cathode have the same geometrical dimensions and are operated at the same temperature. The thoriated-tungsten cathode gives 5000 times more current than the other one. Find the operating temperature. Take relevant data from the previous problem.

The saturation current from a thoriated-tungsten cathode at 2000 K is 100 mA . What will be the saturation current for a pure-tungsten cathode of the same surface area operating at the same temperature? The constant A in the Richardson-Dushman equation is 60 xx 10^4 A m^(-2) K^(-2) for pure tungsten and 3.0 xx 10^(4) A m^(-2) K^(-2) for thoriated tungsten. The work function of pure tungsten is 4.5 eV and that of thoriated tungsten is 2.6 eV .

Light is incident normally on a small plane surface. If the surface is rotated by an angle of 30 about the incident light, does the illuminance of the surface increase, decrease or remain same ? Does your answer change if the light did not fall normally on the surface ?

If the radius of a cylinder is doubled keeping its lateral surface area the same, then what is its height ?