4.4 Use of electrostatics in the real world Flashcards
What 3 technologies do I need to know about?
Microwave ovens, LCDs and electrostatic precipitators
What does LCD stand for?
liquid crystal display
What is a electric dipole?
system of 2 opposite , but equal charges separated by a distance
What happens when a dipole is placed within an electric field?
The two charges experience equal but opposite forces, although resultant force is 0 there will be a twisting effect until parallel to electric field.
Which 2 technologies make use of dipoles within electric fields?
microwaves ovens and LCDs
How does a microwave oven work?
There is an electric field that keeps reversing direction, in which we have food and drink. The water molecules within those are said to be dipoles. When in this reversing electric field the water molecules keep trying to align themselves, however the rate of change is too great and the molecules only collide among themselves. The molecules then gain energy and dissipated it heating the food/drink up.
What can we notice about very dry (water less) food in the microwave? e.g. frozen food
It doesn’t heat up easily
What is the dipole moment?
the product of seperate charges and effective distance between them
What happens in a microwave oven to foods that have a lower dipole moment?
They take longer to heat up
What is the dipole moment measure in?
Cm CoulombMeters
What is the molecules arrangement in an LCD?
They are all in a line
How does an LCD work?
There is different segments and electric field can be manipulated individually for each. When the electric field is on the alignment of dipoles (molecules) alters and changes response of segment. The response is now different and polarisers (change light to one axis) are used. The light going into dipole leaves on the axis of dipole.
What is an electrostatic precipitator?
Devices that remove smoke or dust particles.
In an LCD explain what happens when light passes through the second polariser.
The light passes through 1st polariser, vibrating in one axis. The electric field created changes the alignment on dipoles (usually by 90). This means light hitting the dipoles leaves with the same axis a the alignment of molecules. This would mean light now is in the same axis as the slit on the second polariser so that light can pass through onto the mirror.
In an LCD explain what happens when light doesn’t pass through the second polariser? assume first one lets light vibrate horizontally
- Light travels from the back of the TV toward the front from a large bright light.
- A horizontal polarizing filter in front of the light blocks out all light waves except those vibrating horizontally.
- Only light waves vibrating horizontally can get through.
- A transistor switches off this pixel by switching on the electricity flowing through its liquid crystals. That makes the crystals straighten out (so they’re completely untwisted), and the light travels straight through them unchanged.
- Light waves emerge from the liquid crystals still vibrating horizontally.
- A vertical polarizing filter in front of the liquid crystals blocks out all light waves except those vibrating vertically. The horizontally vibrating light that travelled through the liquid crystals cannot get through the vertical filter.
- No light reaches the screen at this point. In other words, this pixel is dark.
