Question

MY NOTES Three types of charged particles, lets call them A, B, and C, are accelerated and then pass through a velocity selector so that we know they have the same velocity, moving to the right. They then enter a region where the magnetic field is pointing into the paper. Particles A and B are deflected upwards, as shown, while particle C is deflected downwards. The paths of the charges in the field are arcs of circles with the radii being 0.33 m for charge A, 0.60 m for charge B, and 0.16 m for charge C. Charged Particles Into Bubble Chamber (a) What is the sign of the charge on particle A? Positive Negative No Charge (b) What is the sign of the charge on particle C? Positive Negative No Charge (c) Suppose that both the mass and charge of particle C were doubled.. What would happen to the radius of the arc in which it travels? Radius quadruples Radius doubles Radius is unchanged Radius is halved Radius is quartered Other

Answer 1

a) When a charge (q) enter into a magnetic field, the magnetic force acting on it F=q(X) =qvBsin

Where v=velocity of charge., B=magnetic field and = angle between velocity and magnetic field.

In this question =90.

Hence F=qvB.

The charges begin to rotate around the magnetic field by Fleming's left hand rule. That is Force is perpendicular to both v and B.

Here we can consider that charges are moving along positive X axis (velocity ).As charges A and B are deflected upwards(Force along positive Y axis), the charges on A and B are positive because magnetic field is along negative Z axis. (Fleming's left hand rule )

b)As charge C is deflecting downwards, its charge is negative. (Force becomes opposite )

F=-q(X)

c) Radius of path of charge

r=mv/qB

Where m=mass of charge, v=velocity, q=magnitude of charge and B=magnetic field

Hence as mass(m) and charge(q) are doubled, radius does not change because numerator and denominator are doubled. That is radius of arc of charge C has no change.