Force Due to Magnetic Field You will use

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Fay Lee
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1 Force Due to Magnetic Field You will use Units: 1 N = 1C(m/s) (T) A magnetic field of one tesla is very powerful magnetic field. Sometimes it may be convenient to use the gauss, which is equal to 1/10,000 of a tesla. Earth s magnetic field, at the surface, varies but has the strength of about one gauss.

Magnetic Force on a moving charge If a MOVING

The conditions for the force are: Must have a

Charge must be positive or negative Charge

2 Magnetic Force on a moving charge If a MOVING CHARGE moves into a magnetic field it will experience a MAGNETIC FORCE. This deflection is 3D in nature. The conditions for the force are: Must have a magnetic field present Charge must be moving Charge must be positive or negative Charge must be moving PERPENDICULAR to the field. Magnetic Force on a moving charge perpendicular vectors This force is always perpendicular to both the magnetic field and velocity

3 Problem A proton moves with a speed of 1.0x10 5 m/s through the Earth s magnetic field, which has a value of 55 T at a particular location. When the proton moves eastward, the magnetic force is a maximum, and when it moves northward, no magnetic force acts upon it. What is the magnitude and direction of the magnetic force acting on the proton? Problem A proton moves with a speed of 1.0x10 5 m/s through the Earth s magnetic field, which has a value of 55 T at a particular location. When the proton moves eastward, the magnetic force is a maximum, and when it moves northward, no magnetic force acts upon it. What is the magnitude and direction of the magnetic force acting on the proton? The direction cannot be determined precisely by the given information. Since no force acts on the proton when it moves northward (meaning the angle is equal to ZERO), we can infer that the magnetic field must either go northward or southward.

Direction of the magnetic force? Right Hand Rule #1 (RHR#1) RHR#1 determines the directions of magnetic force, velocity of the charge, and the magnetic field.

4 Direction of the magnetic force? Right Hand Rule #1 (RHR#1) RHR#1 determines the directions of magnetic force, velocity of the charge, and the magnetic field. Given any two of theses, the third can be found. Using your right-hand: point your index finger in the direction of the charge's velocity, v; point your middle finger in the direction of the magnetic field, B. Your thumb now points in the direction of the magnetic force, F magnetic. Use your left-hand if you have an electron Force Due to Magnetic Field A proton enters a uniform magnetic field of magnitude 0.25 T, consisting of field lines pointing into the page, with a horizontal velocity 4.0x10 6 m/s [right]. What is the magnitude and direction of the instantaneous force exerted on it? How would this change if it were an electron moving through the field? B (into the page) + v

5 Suppose we have an electron traveling at a velocity, v, entering a magnetic field, B, directed into the page. What happens after the initial force acts on the charge? Suppose we have an electron traveling at a velocity, v, entering a magnetic field, B, directed into the page. What happens after the initial force acts on the charge?

6 Suppose we have an electron traveling at a velocity, v, entering a magnetic field, B, directed into the page. What happens after the initial force acts on the charge? Magnetic Force and Circular Motion

7 Magnetic Force and Circular Motion The magnetic force is equal to the centripetal force and thus can be used to solve for the circular path. F mag = F c If the radius is known, could be used to solve for the MASS of the ion. This could be used to determine the material of the object. A charged positive ion has a mass of 2.5 x kg. After being accelerated through a potential difference of 250 V, the ion enters a magnetic field of 0.5 T, in a direction perpendicular to the field. Calculate the radius of the path of the ion in the field. Hint: Need to use V=W/q to solve for velocity (use W = KE), then solve for r

Mass Spectrometers Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the mass-tocharge ratio of

The ratio of charge to mass of the particles is calculated by passing them through ELECTRIC and MAGNETIC fields in a mass spectrometer. M.S.

8 Mass Spectrometers Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the mass-tocharge ratio of charged particles. A sample undergoes chemical fragmentation, thereby forming charged particles (ions). The ratio of charge to mass of the particles is calculated by passing them through ELECTRIC and MAGNETIC fields in a mass spectrometer. M.S. Area 1 The Velocity Selector When you inject the sample, you want it to go STRAIGHT through the plates. Since you have an electric field you also need a magnetic field to apply a force in such a way as to CANCEL out the electric force caused by the electric field. F mag = F e

M.S. Area 2 Detector Region After leaving region 1 in a straight line, it enters region 2, which ONLY has a magnetic field. This field causes the ion to move in a circle separating the ions by mass.

9 M.S. Area 2 Detector Region After leaving region 1 in a straight line, it enters region 2, which ONLY has a magnetic field. This field causes the ion to move in a circle separating the ions by mass. This is also where the charge to mass ratio can then by calculated. From that point, analyzing the data can lead to identifying unknown samples. Charge to Mass Ratio of an Ion in a MS F mag = F c F mag = F e and then OR FROM combining E electric = E kinetic with F mag = F c and then Where: ε = Electric Field Strength (N/C) B = Magnetic Field Strength (T) V = Potential Difference (V) r = radius of circular path (m) q = charge on ion (C)

10 The operator of a mass spectrometer produces a beam of doubly ionized (2+) neon atoms. They first are accelerated by a potential difference of 34 V. Then, as the ions pass through a magnetic field of T, the radius of their path is 53 mm. Determine the mass of the neon atom to the closest whole number of proton masses (1.67 x10-27 kg) Complete all the problems on pages 80-81

Chapter 27, 28 & 29: Magnetism & Electromagnetic Induction

Chapter 27, 28 & 29: Magnetism & Electromagnetic Induction The Magnetic Field The Magnetic Force on Moving Charges The Motion of Charged Particles in a Magnetic Field The Magnetic Force Exerted on a Current-Carrying