Find who takes the charge

1 · Find what pushes the charge

Beginner

According to this theory, what pushes the charge from one grain to the other?

Electrons trapped at the surface A voltage born of a temperature gap Ions from hydroxide layers

2 · Work out the new voltage

According to equation 4 of the paper, for the same heat per impact and the same number of impacts, the voltage between a small grain (radius R_s) and a large one (radius R_l) scales as R_s⁻³ − R_l⁻³.

A grain of radius 100 micrometres hits one of radius 200 micrometres. The small one is replaced by a grain of radius 50 micrometres.

Intermediate

By what factor is the voltage multiplied?

2 8 9

3 · Weigh two twin grains

The model deposits the same heat on both surfaces in contact. Two identical quartz grains, each of radius 100 micrometres, collide thousands of times.

Expert

What does the model predict for their charge?

No charge transfer A negative charge on the grain that strikes A charge whose direction depends on the sign of S

4 · Follow the heat over thousands of impacts

For a single impact, the size of the voltage depends on S/k, where k is the material's thermal conductivity. The authors then move on to repeated impacts (equation 3).

Expert

What takes the place of the conductivity k?

The duration of each impact The heat capacity of the grain The contact area between the grains

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