How does a bubble-jet printer work

A bubble-jet printer is one of the more useful and versatile inventions of the last decade. The active component of the printer is the head through which liquid ink passes before striking the page. The head moves from side to side over the page. When 

The head is commonly about an inch wide, and consists of a row of hundreds of tiny pores (or capillaries ), each connecting the ink reservoir (the cartridge) and the page. The signals from the computer are different for each pore, allowing different parts of the page to receive ink at different times. By this method, images or letters are formed by the printer. 

Just before the computer instructs the printer to eject a bubble of ink, the heater is activated, causing the air pocket to increase in temperature T at quite a rapid rate. The temperature increase causes the air to expand to a greater volume V. This greater volume increases the pressure p within the air pocket. The enhanced air pressure p is sufficient to eject the ink bubble from the pore and onto the page. This pressure-activated ejection is similar to spitting. 

This ejection of ink from a bubble-jet printer ingeniously utilizes the interconnectedness of pressure p, volume V and temperature T. Experiments with simple gases show how p, T and V are related by the relation 

If there is exactly 1 mol of gas, the pressure is expressed in pascals (Pa), the temperature is in kelvin and the volume is in cubic metres (both SI units), then the value of the constant is 8.314 JK-1 mol-1. We call it the gas constant and give it the symbol R. (Some old books may call R the universal gas constant , molar gas constant or just the gas constant . You will find a discussion about R on p. 54) More generally, Equation (1.12) is rewritten as 

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