Question

It is possible, using basic lab equipment, to observe the force that a magnet exerts on current in a wire. Equipment:DC Power Supply (3A preferred), Long Banana wire, Large Pasco C Magnet, 1 gm sensitivity food scale. (There will only be a few systems set up. Your TA's will direct you in sharing their use.) Theory: The force due to a magnetic field on a straight wire carrying a current in a uniform B field is: F = iL x B , where L is the length of the segment of wire with which the field interacts. x х х х X X X Consider a length of straight wire that passes through a region of uniform field (B = a T) as sketched to the right. Take the length of the field region to be b cm and the length of the wire to be L cm. The current is i = c A. The field is into the paper. Y << X Current * X X х x X X х 1) Calculate the force exerted on the wire above in terms of the parameters a, b, c, L. Include the direction of the force (up, down, into paper, out of paper, left, right...). N (direction) 2) You will use a scale to measure the force on the wire, but scales frequently report mass (or “kg force", kgf), rather than Newtons (9.8N=1 kgf). 3) Set up the DC power supply so you can pass the maximum current (2 or 3 A) through the long banana wire. (Then turn the power supply off.) The strength of your magnet is approximately 0.18 T. Place the large magnet on its feet (open side up) on the scale. Set the scale to measure grams. Press and hold the "Tare" button to zero out the mass-force of the magnet itself. Hold the wire so it passes horizontally between the poles of the magnet. 4) Turn on the current and note the change in mass-force. (You will need three hands to hold the wire and turn on the current, so a partner is useful here.) Reverse the wire or current direction and repeat. Write the absolute value of each measurement in the boxes below and find their average. (This procedure decreases the effect of an error in the scale tare.) +5gf & -5gf )/2= 5) List the values of relevant parameters for your measurement here. Magnetic field= 0.1 T ; Length of field regiona 1 m ; Current; 3A 6) Compare your observed force to the force you estimate based on the relation in part 1 above. Is the measurement within uncertainty of your theoretical estimate?

Answer 1

F = Bil = a.c.b. abc l length of wire inside magnetic field. Mass abe 9.8 o.1x dilx 3 9.8 0.003 kgf when direction of current is reserved then magnitude of fore not direction is changed changed only