2 Answer ALL questions in the spaces provided. 1 A student set up the apparatus shown. A length of rigid wire was held horizontally by a clamp in a uniform magnetic field of flux density B. The circuit connected to the rigid wire is also shown. rigid wire A clamp stand balance rigid wire magnets l With the switch open, the balance was set to zero. When the switch was closed a current I in the circuit was recorded by the ammeter and the reading on the balance increased. (a) The length l of wire in the magnetic field was 15.5 cm. When the current in the circuit was 4.55 A, the reading on the balance increased by 5.65 g. Calculate the magnetic flux density B in the region of the rigid wire. (3) ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... B = ....................................................... Turn over 3 (b) The student wrote the following statement “The balance could read to the nearest 0.01 g, which makes my values for the magnetic force both accurate and precise.” Comment on this statement. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 1 = 6 marks)