electromagnetic induction

International Year 1 – Electronics Engineering International Study Centre – University of Sussex Electromechanics Summer 2017 : Coursework 2 – Electromagnetic Induction Hand out date Monday 3 July 2017 Submission date Friday 21 July 2017 Coursework weighting 20% of module Set by Dr Kingsley Sage Instructions 1. Please answer all of the questions. 2. Show your workings. You can still get credit for workings even if your answer is not correct. 3. Please submit your coursework on the date and time shown. There are penalties for late submission. 4. Plagiarism is a very serious matter. Do not copy another student’s work. Please ask for help from your tutors if you do not understand the questions or you need help in understanding how to solve the problems . 5. The quality of English that you use in your answers will be assessed as part of this coursework . Try to make any arguments or discussions as clear as possible . Think about using diagrams to help explain your answers. ../ Q1 1(a) Find the maximum va lue of the voltage induced in a coil of 200 turns by a magnetic flux = Ф if Ф = 400 Wb and the frequency is 5 0Hz . 1(b) 100 turns of insulated copper wire are wrapped around an iron core of cross -sectional area 0.001m 2. The circuit is complet ed by connecting the wire to a 2 0 Ω resistor. The magnetic field along the coil axis is made to change from 1 T in one direction to 1 T in the other direction. What is the total charge that flows through the resistor in this process? 1(c) A conductin g loop with area 0.15 m2 and resistance 6 Ω lies in the x-y plane. A spatiall y uniform magnetic field points in the z direction. The field varies with time according to : = 2− where a = 2 T/s 2 and b = 8 T. Find the loop current: (i) when t = 3s (ii) when Bz = 0. 1(d) A 10 -turn coil 1 cm in diameter is rotated at 10 rev/s about an axis perpendicular to a uniform magnetic field. A voltmeter connected to the coil through rotating con tacts reads a peak value of 360 V. What is the magnetic flux density ? Q2 2(a) A square wire loop 3 m on a side is perpendicular to a uniform magnetic field of 2T. A 9 V light bulb is in series with the loo p, as shown below . The magnetic field is pointing into the page. The magnetic field is reduced steadily to zero over a time t. (i) Find t such that the light will shine at full b rightness during this time. (ii) Which way will the loop current flow? 2(b) A square conducting loop of side s = 0.5 m and resistance R = 5Ω move s to the right with speed v = 0.25 m/s as shown in the diagram overleaf . At time t = 0 its rightmost edge enters a uniform magnetic field B = 1 T pointing into th e page, as shown below. The magnetic field covers a region of width w = 0.75 m. Plot : (i) The cu rrent; and (ii) the power dissipation in the loop as functions of time, taking a clockwise current as positive and covering the time until the e ntire loop has exited the field region. Q3 A solenoid 2 m long and 30 cm in diameter consists of 5000 turns of wire. A 5 -turn coi l with negligible resistance is wrapped around the solenoid and connected to a 180Ω resistor, as shown below . The direction of the current in the solenoid is such that the solenoid’s magnetic field points to the right. At time t = 0 the s olenoid current begins to decay exponentially, being given by : = 0 − where 0 = 85A, τ = 2.5s and t is the time in seconds. (i) What is the direction of the current in the resistor as the solenoid current decays? (i) What is the value of the resistor current at t = 1s and t = 5 s? Q4 The diagram below shows a pair of parallel conducting rails a distance ℓ apart in a uniform magnetic field B. A resistance R is connected across the rails, and a conducting bar of negligible resistance is being pulled along the rails with velocity v to the righ t. (i) What is the direction of t he current in the resistor? (ii) At what rate must work be done by the agent pulling the bar? END. Dr Kingsley Sage [email protected]