H216 Electromagnetism-Tutorial (wSolutions)(1718).student

Topic 16: Electromagnetism Page 1 9749 H2 Physics Tutorial Solution Electromagnetism Tutorial Solution Discussion Magnetic field lines D1 (a) The figure illustrates the patterns of the magnetic flux due to a current in a solenoid. (i) On the figure, draw arrows to show the direction of the magnetic field in th e solenoid. [1] (ii) The coils of wire on an electromagnet are usually wound on a ferrous core. State two properties of the core which are important in its use in an electromagnet. [2] It can be easily magnetized / de-magentised, when the current is switched on/off. It concentrates the magnetic field lines and thereby increasing the magnetic flux density at the centre of the coil. (b) A loosely-coiled spring is suspended from a fixed point as illustrated on the right. Electrical connections are made to the ends of the spring. When a current is switched on in the spring, there is a small change in the length of the spring. flexible lead (i) Magnetic field lines

Topic 16: Electromagnetism Page 2 9749 H2 Physics Tutorial Solution (i) On the figure, indicate the direction of the current in the individual turns of the spring and the direction of the magnetic field. [2] (ii) On the figure on the right, draw the pattern of the magnetic field due to a straight current - carrying wire. [1] For this question, check to ensure that the circles they draw are further and further apart. The magnetic flux density should become weaker (field lines further apart) as the distance from the wire increases. Also, it’s a 3D plane, the shape of the field line is an ellipse.

Topic 16: Electromagnetism Page 3 9749 H2 Physics Tutorial Solution D2. X and Y are two coaxial circular coils lying on a table. O, P and Q are three points on the table. Initially, there is a constant current in coil X and no current in coil Y. A small current is now passed through coil Y, which decreases the magnitude of the magnetic flux density at O. How does the magnitude of the flux density changes at P and Q? P Q A Decreases Decreases B Decreases Increases C Increases Decreases D increases Increases Solution: Choose an arbitrary current direction in wire X. Draw the magnetic field pattern due to the current in wire X at the positions O, P, Q. Choose an arbitrary current direction in wire Y to get the resultant magnetic field effect in O. D3. Force on a current-carrying conductor in a magnetic field A straight wire of mass 10 g and lengt h 5 cm is suspended from two identical springs which, in turn, form a closed circuit as shown. The total resistance of the circuit is 12 . Each spring is stretched a distance of 0.5 m under the weight of the wire. When a magnetic field is turned on, dire cted out of the page (indicated by the dots), the springs are observed to stretched an additional 3 cm. (a) Draw a free body