How to unload a charged isolator

Big Bang Physics 6, textbook

Fields 103 The electric field 25 The capacitance can be increased by placing an insulator between the plates. Why? Due to its polarization, the field line density and thus the voltage between the plates decreases with the same charge (Fig. 25.33), we assume from 1 to 0.5V. When you bring the plates back to 1V, they are now charged twice as much as before. Double charging at the same voltage means double the capacity. Some materials can increase the capacity by a factor of 10 5! What happens if you pull apart the plates of a charged capacitor? It's amazing, but it increases the tension. Why? You need energy to pull it apart because the plates are charged in opposite directions. Lots of keys In a computer keyboard there is a capacitor under each key (Fig. 25.31 a; F19). The plates are, as it were, "printed" on two layers of plastic. The distance to the lower layer and thus to the second plate is reduced by pressing the button and thus also the voltage of the capacitor concerned. So the PC knows which key you have pressed. A sensor key (b) works in a very similar way. With her, however, the finger acts as a second plate. It is very similar to the sensor key with the capacitive touchscreens that are used on most smartphones and tablets (F19). Here, however, there are around 100 plates under the display, which means that the position of the finger can be determined very precisely (Fig. 25.32). i Fig. 25.31: a) The disks under the buttons are the plates of the capacitors. b) A sensor key is a plastic-insulated plate. Together with the finger, this becomes a capacitor. Fig. 25.32: On smartphones and tablets there are plates under the actual display, which act like the lower halves of plate capacitors when touched. Fig. 25.33: If an insulator is placed between the plates, it is polarized (b). As a result, some of the field lines end on its outside, and the field between the plates is weakened. This also reduces the tension. are. The energy cannot be lost, it is then stuck in the electric field. Because the charge does not change, the voltage has to increase. This is why the spark would be stronger in the event of a short circuit after being pulled apart (F22). Conversely, the tension decreases when you push the plates together. This is used, for example, with a PC keyboard and touchscreen. Info: Lots of keys Relatively little energy is stored in a capacitor. But if you discharge this in a very short time, almost unbelievable performance can be produced. The defibrillator or a camera flash are based on this principle (F21; see also F27). Summary The capacity of a capacitor indicates how many charges can be stored with the same voltage. This can be changed by the distance and by inserting an insulator. Z The electric field Could charged bodies exist in an unknown universe without an electric field? L With what force do protons and electrons attract each other in the hydrogen atom? With what force do the two protons in a helium nucleus repel each other? Could you use muscle power to detach the electron and hold the protons together? L Calculate the amount of energy they contain for the following battery types (all have 1.5V) and how high you could lift 1 kg with it: AAA 4000 Coulomb, AA 9400 C, C 28,000 C, D 59,500 C. L How could one find an equation for dissipate the energy stored in a capacitor? You only need the equation W = Q · U and a basic consideration. L What power and amperage occurs when discharging a defibrillator? Assume the discharge time is 5ms, the charge energy 360 J and the voltage 2000V. What is the minimum capacity of the capacitor? L 25 F23 S1 F24 S2 F25 W2 F26 W2 F27 W2 For testing purposes only - property of the publisher öbv

Made with FlippingBook