**P. 4241.** A sample of ideal gas is taken through the cyclic process shown in the *figure. *

*a*) What is the relation between *T*_{1}, *T*_{2} and *T*_{3}?

*b*) Express the efficiency of the heat engine which carry out this cyclic process in terms of and .

*c*) In case of air between what values can this efficiency vary?

(4 points)

**P. 4242.** A candle is burning in a vertical cylinder standing on the table. The inner wall of the cylinder has a reflexive surface. The height of the cylinder is 30 cm, its diameter is 12 cm, and the centre of the candle light is at a height of 14 cm, 2 cm away from the axis of the cylinder. From which direction will the image of the candle light, which becomes three times wider, be on the top of the cylinder?

(5 points)

**P. 4243.** The number of turns of a solenoid (straight coil) of length *L*=0,5 m is *N*=2000, the area of its cross section is *A*=16 cm^{2}, and it has an iron core of relative permittivity of _{r}=2500. At a moment the current in the coil changes at a rate of 100 A/s. What is the induced voltage in that long straight wire of length 2=20 cm (the wire is next to the centre of the coil)

*a*) which is perpendicular to the axis of the coil, if its two ends are equidistant from the coil, and its centre is at a distance of from the coil?

*b*) which has the same direction as the previous one, and one of its end is at a distance of from the axis of the coil?

(5 points)