Dean is hunting in the Northwest Territories at a location where earths magnetic field is 7.0x10^-5T. He shoots by mistake at a duck decoy, and the rubber bullet he is using acquires a charge of 2.0x10^-12C as it leaves his gun at 300 m/s, perpendicular to earths magnetic field. What is the magnitude of the magnetic force acting on the bullet?
The magnetic force acting on an object of charge q is [tex]F=qvB \sin \theta[/tex] where q is the charge v is the speed of the object B is the magnetic field intensity [tex]\theta[/tex] is the angle between the directions of v and B.
In our problem, the direction of the bullet is perpendicular to the magnetic field, so [tex]\theta=90^{\circ}[/tex] and [tex]\sin \theta=1[/tex], so we can ignore it in the formula.
Therefore, we can use the data of the problem to calculate the magnetic force on the bullet: [tex]F=qvB=(2.0 \cdot 10^{-12}C)(300 m/s)(7.0 \cdot 10^{-5} T)=4.2 \cdot 10^{-14} N[/tex]
