The diagram shows an air filter which uses charged collecting plates to remove dust from the air of a workshop.
The air intake passes through a charged, ionising grid which attracts dust particles, cleaning the air which is then returned back into the workshop.
A dust particle of mass 6.7 × 10–15 kg enters the region between the collecting plates travelling horizontally with an initial velocity of 11 m s–1. The particle carries a charge of 2.6 × 10–18 C.
Assume that the dust particles move horizontally between the plates.
(a)
Determine the electrostatic force acting on the particle.
Some particles are not caught by the air filter, but pass straight through. Others are caught by the filter. The particles are identical in mass and charge, and they all travel parallel to the plane of the plates. The plates are initially completely clean. Assume the particles are evenly vertically distributed.
(b)
Deduce the percentage of dust particles which will be 'trapped' by the negatively charged plate. Ignore the effect of gravity.
As the air filter operates, there is a build up of particles on the negative plates. The gap between the plates therefore becomes narrower, by up to 10% of its initial height.
(c)
Discuss whether this narrowing makes the filter more or less effective at removing dust particles.
Two charged objects X and Y are made to circle a point O. X and Y are at a distance, d = 1.8 × 10−8 m and they have equal masses, where m = 1.7 × 10−9 kg. The objects carry an equal but opposite charge, where the magnitude q = 3.2 × 10−19 C.
An experiment to determine the charge on an electron is shown.
Negatively charged oil drops are sprayed into a region above two parallel metal plates which are separated by a distance, d. The oil drops enter the region between the plates.
(a)
A potential difference V is applied which causes an electric field to be set up between the plates.
(i)
Using the sketch below, which shows one oil drop falling between the plates, show the electric field between the plates.
[1]
(ii)
Hence or otherwise explain why the oil drop stops falling when V is increased.
Two oil drops are suspended between the plates at the same time. The oil drops can be considered as identical point charges with mass 1 × 10−13 kg which are spaced 2.2 mm apart.
(c)
Calculate the electrostatic force between the drops.
Describe and explain the expected observations as the potential difference increases above 5000 V, using a mathematical expression to justify your answer.
Using the calculated values from parts (a) and (b)
(i)
Determine how long it would take an electron travelling in a wire of this material to get from London to New York, a distance of approximately 5 500 km. State your answer in a reasonable unit for the amount of time.
[1]
(ii)
Hence explain how it is possible to send information by electrical signals across these distances.
[1]
(iii)
The electrons are travelling with either constant velocity or constant acceleration. Select the most likely option and explain your answer.
