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A water bath in a lab has a power rating of 2.5 kW. It was used to heat tap water at 17°c to a temperature of 37°c for a biology experiment on enzymes. It took 22mins and 45 secs before the water reached the right temperature. The bath contained 30 litres of waterThe specific heat capacity of water is 4.2 J kg-1K-1

Total energy used by heating element during the heating period.

Power= 2.5 kW

Time= 22 mins and 45 secs= 1365 seconds

Total energy used (energy output) = 1365x 2.5

= 3412.5 joules

Useful energy absorbed by water

Mass of substance= 30 litres

Specific heat capacity= 4.2 J kg-1 K-1

Temperature rise= 20°c

Energy absorbed= 30x4.2x20

= 2520 Jkg-1K-1

Efficiency= 3412.5/2520 x 100

= 73.8 %

Energy conversions

1. Electric fire

Electrical energy à heat energy, light energy + sound energy

2. A car

Potential energy (petrol) à kinetic energy, sound energy, + heat
energy.

The electric fire is more efficient because the heat energy that it emits is useful. Whereas in most other energy conversions, such as the car, heat energy is actually a waste product and is not used.

Task 6

The microscope is designed to magnify an object/specimen that is placed onto the stage.

A mirror at the bottom of the microscope projects the light through a hole in the stage and through the object. The objective lens picks up this light and magnifies it. The light then continues through the tube to the eye piece, which magnifies the image more before we see it. Most microscopes have more than one objective lens, and these can be changed to increase or decrease the magnification. The objective lens can also be moved closer, or further away from the object to focus it. This is done using the course focus knob. The fine focus knob can also be used to focus the image further. The stage is used to place the object on, and the stage clips to keep the object in place and top it moving around.

PH meters are designed to tell you the pH of a solution quickly and efficiently. They consist of three main parts; the sensing electrode, the referencing electrode and the electronics of the meterThe special glass on the end of the sensing electrode senses H+ ions and a millivoltage is generated. The solution in the bottom of the pH
meter that touches the special glass picks up this signal, a pure silver wire dipped in silver chloride passes this signal from the solution to the electrodes cable/connector.The filling solution in the reference electrode has oH- ions in it. This generates a millivoltage which is passed on in the same way as in the sensing electrode.

The millivoltages are then passed on into the electronic part of the pH meter. The pH meter then takes the inputs from the sensing electrode and the referencing electrode and compares the two values to get a result millivolt reading. The reading in mV is then converted into a pH reading. 本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。