External Combustion Engine

Q Describe the working of four strokes of petrol engine?

• The working of a patrol engine is divided into four stages.
• Intake stroke
• In this stroke, the intake valve is open and exhaust valve is closed.
• The mixture of patrol vapor and air enters the cylinder through the intake valve by the downward movement of the piston.
• Compressions stroke.
• In this stroke, both of the valves are closed.
• The patrol air mixture is compressed to 1/8 of its original volume by the upward movement of the piston.
• Power stroke
• Spark plug will produce a little spark.
• The patrol, air mixture, burns rapidly with a little explosion producing a large volume of gases and a lot of heat.
• The heat that’s produced expands the gases rapidly.
• The rapid expanding gases exerts pressure on the piston due to which the piston moves outward.
• The moving piston pushes the piston rod and rotates the wheel through crank shaft.
• Exhaust stroke
• In the stroke the intake valve is closed and exhaust valve opens.
• Due to the momentum gained by the wheel in the power stroke the piston falls back and expels the spent gases, through exhaust valve into the atmosphere.
• This cycle is repeated again and again, and the continuous motion of wheels is obtained.

Q Draw the diagram of power stroke of a steam engine?

Q Define 1 kWh and how is it related to Joule?

• 1 kWh is the energy supplied by a weight of working off 1000W in one hour
• 1 kWh = 3.6 X 10 pow 6 Joule

Q If one unit of electric energy goes into heating 50 L of water, calculate the rise in temperature?

• M= 50kg
• C= 4200 J/kg
• E = 3.6 x 10 pow 6
• E = MC DeltaT
• DeltaT = 17.1 degree Celsius 

Q In a house 2 electric bulbs each off 100 watt are used for 15 hours and our electric heater of 750 W is used for 10 hours every day. Calculate the cost of using the bulb and heater for 30 days if the cost of one unit is 2?

• E = npt (no of days)
• E = 30X100X15
• E = 45000kwh
• E = 45kwh
• Energy by one bulb is equal to 45KWH.
• Energy consumed by two bulb is equal to 90 KWH.
• Energy consumed by electric heater is equal to 225KWH.
• 30x750/1000x10
• Total energy consumed is equal to 90+225 equal to 315KWH.
• Cost of one KWH is equals to rupees 2.
• Cost of 315KWH is equal to 2 x 315 = 630 Rs.

Q Joules experiment with diagram?

• Joule’s experiment
• Set up the apparatus as illustrated above.
• The calorie meter is filled with water, and the initial temperature of the water is noted by the thermometer. 
• The weights are allowed to fall through the pulley simultaneously from a certain height.
• The falling weight rotate the pedal.
• The rotating pedal in turn Starts churning the water.
• The kinetic energy of falling weights rotate the spindle, which in turn rotate the wooden drum.
• J= W/Q = 2mgh/MXcXdeltaT

Q Define de efficiency of a heat engine?

• Efficiency of a heat engine is equal to 
• heat converted into work/total heat taken in.
• Efficiency of heat engine is always less than one because heat energy can never be completely converted into mechanical energy.

Q How can you sail a boat against the direction of wind?

• This can be done by using two sails in the same boat, which are controlled by a steering device called radar.
• The two sails are held at an angle to one another. One of the Sail diverts the direction of the wind while the other sail propels the boat.

Q What is the function of reflector and glass sheet in a solar cooker?

• The reflector is used to increase the efficiency of a solar cooker. It increases the area over which the solar energy is collected so that more and more heat rays of the sun may enter into the box and solar cooker works more efficiently.
• Glass sheet allows to sort the shorter wavelength infrared rays, coming from the sun to pass through it, but does not allow the longer wavelength infrared rays to get out from the box. Due to this greenhouse effect the heat inside, the box is retained by eight and the temperature rises appreciably.