Name…………………….
Class…………..
(
/18)………..%………..
Lesson 14 questions – Examples of circular motion
1
Read the short passage before answering the question below.
Figure 1.1 shows a section of a mass spectrometer. A beam of identical positivelycharged ions, all traveling at the same speed, enters an evacuated chamber through a slit
S. A uniform magnetic field directed vertically out of the plane of the diagram causes the
ions to move along a semicircular path SPT. The beam exits the chamber through the slit
at T
.
Fig 1.1
a)
i)
On Fig.1.1, draw an arrow to indicate the direction of the force on
the ion beam at P.
(1)
ii)
Name the rule you would use to verify that the ions are positively
charged.
…………Fleming’s LHR…………………………………………………………………
………………………………………………………………………………………… (1)
iii)
Explain why the ions follow a circular path in the chamber.
……Constant force on charge caused by magnetic field………………………
……perpendicular to path of ions/ towards center of circle………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………… (2)
b)
Describe and explain the changes to the path of the ions for a beam of ions
of greater mass but the same speed and charge.
……Larger semicircle……………………………………………………………………
……from F=ma……………………………………………………………………………
……so same force but bigger mass means less centripetal acceleration……………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………………
………………………………………………………………………………………… (3)
Name…………………….
Class…………..
c)
(
/18)………..%………..
The speed of the singly charged ions is 3.0 x 105ms-1 in the magnetic field
of flux density 0.60T. The mass of each ion is 4.0 x 10-26 kg and the force
on each ion in the beam in the magnetic field is about 3 x 10-14N.
Calculate the radius of the semicircular path.
F=mv2/r
r=(4.0 x 10-26 x (3.0 x 105)2)/3 x 10-14
Radius = ……0.125………. m (3)
2
A compact disc (CD) player varies the rate of rotation of the disc in order to keep
the track from which the music is being reproduced moving at a constant linear speed of
1.30ms-1. Calculate the rates of rotation of a 12.0cm disc when the music is being read
from
a)
The outer edge of the disc. Give your answers in both (i) rad s-1. and (ii)
-1
Rev min
i)v=rω
ω=v/r
= 1.3/0.06
= 21.7 rad s-1
ii)(21.7/2π)60
i)
rate of rotation = ……21.7………………….. rad s-1 (2)
ii) rate of rotation = ……207………………….. Rev min-1 (2)
b)
A point 2.55 cm from the center of the disc. Give your answers in both (i)
rad s . and (ii) Rev min-1
-1
i)v=rω
ω=v/r
= 1.3/0.0255
ii)(51/2π)x60
i)
ii)
rate of rotation = ………51……………….. rad s-1 (2)
rate of rotation = …………487…………….. Rev min-1 (2)