PHYS227N S13 COOK Test 4 - OLD DOMINION UNIVERSITY PHYSICS...

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Unformatted text preview: OLD DOMINION UNIVERSITY PHYSICS 227N/232N, University Physics I Spring 2013 Fourth Examination 8:30 — 10:20am Tuesday 09 April 2013 PROFESSOR: Dr. D. C. Cook Answer all-4 questions: The number of marks for each question is shown. All questions should be answered on the examination paper. If more space is required, attach sheets to paper. Text book may not be used. This examination will be 15% of the total c s assessment Honor Pledge Signature Candidate's Mummy-— CONSTANTS AND E UATION S 80 = 8.85 10'” C2 N" m'2 1nC = 10'9 C 1pc = 10'6 C k =1/41reo=9.0109Nm2C‘2 Q=cv e= 1.6x 10"9c me=9.11x10'3' kg mp=1.67x10'27kg Fc = (k q,q2/r2) 1‘ V = IR K = ‘/2 mv2 Fc = mv2/r = mmzr T = 1ff= 21r/(o E=(kq,/r2)t‘ P=VI UE=qV U = k qqu /r R = ple [.10 = 41: x 10'7 Wb A" m'I V=kq2/r FB=quB FB=ilXB B=uuni (DE = i E.dS = q/so (DB =1 B.dS I B.dl = poic ——- - N d(I>Bz’dt Area: Rectangle A=LxW Circle A=an Triangle A=‘/2 Base x Height Circumference: Circle 0 = 2m 1. MAGNETIC FORCES AND FIELDS: GENERAL QUESTIONS. (30 marks) Circle the correct answer (i) A proton is moving at constant speed along the positive y-axis and in a constant magnetic field that is along the positive z—axis. The magnetic force on the proton is (A). along the +x-axis (B) along the +y-axis (C ) along the +z-axis along the -x-axis along the -y-axis ) along the —z-axis (G) There is no magnetic force on the proton (ii) One. horizontal wire runs from lefi to right across the page and carries a current of 15A from left t I right. A single proton travels parallel to the wire from right to left. The magnetic force on fiproton is (A . towards the wire. away from the wire ‘ zero (D) out of the page (E) into the page '35: L_‘ (F) parallel to the proton’s ‘ " g I . (G) opposite to the ’s,motion. .. infirm.“ “3‘ _ w .u- “ (iii) A horizontal current carrying wire (in the plane of the page) is placed in a constant agnetic field as shown below. The magnetic force at point A on the wire is (A) to the right (B ) downwards ® B® I ‘ into the page A upwards '= to the left ® ® (F out of the page (iv) The figure on the right shows a single loop of wire with \/ 6 current I flowing through it. 1 " Fill in the direction of the induced magnetic field at each of the 6 small circles. (v) W 'ich of the following is able to determine whether it is positive or negative charges that move thr gh a conductor? Voltmeter Faraday’s Law Galvanometer (D) Hall Effect (E). Lenz’ Law (F). Ammeter (vi) An electron is moving in circle in a uniform ® ® B magnetic field with a circular trajectory as shown. / Draw one velocity vector for the electron on the diagram. 69 (8) (vii) Write True (T) or False (F) next to each of the following 10 statements. I / (a) A proton is always deflected as it moves in a magnetic field. E _ (b) Electrons and protons moving with the same velocity at right angles L/ through a magnetic field will experience the same magnitude of magnetic force. T (c) Electrons and protons moving with the same velocity at right angles through L/ a magnetic field will have circular orbits of the same radius. E (d) It is possible for a charge to move through a combined magnetic and electric field without being deflected. j (e) A current carrying conductor placed in and at right angles to a magnetic field will experience a magnetic force. ‘ (D An electric current can be generated by rotating a loop of wire in a / magnetic field. '- (g) Ampere’s Law is used to calculate the electric field close to a current carrying conductor. (h) Two parallel wires carrying current in opposite directions will repel each other. a ' (i) The magnetic field inside a solenoid is inversely proportional the radius of the solenoid. (j) A current can be generated by pulling a loop of wire into a magnetic field "1" \ (viii) A solenoid of length of 1.50m and cross-section area of 500cm2 contains 3000 turns of wire carrying 2.50 A of current. What is the magnetic field generated at the center of the solenoid? \/ 3.2x 10'3 T. (B 6.3 x 10'3T 9.5 x 10'3T (D) 11.4 x 10'3 T (E) 12.6 x 10‘3 T (F) 18.9 x 10'3 T End Q1. l ) i t f 2. CHARGE IN A MAGNETIC FIELD. (25 Marks) A proton travels at right angles into a uniform magnetic field of magnitude 2.50 T, with a speed of 1.5mm7 m/s. (a) Calculate the radius the proton’s circular orbit in the magnetic field. Wt :(BUC‘“*‘U“C\<U):?/Wfl #wfmfi I: ' "\‘k\ (‘ WW9 "L 70mm {(Q.S\3( \ . L91: r 7 / ANSWER: r: o . o in (b) What is angular frequency of the proton? F WY,” 3 J5 '-.3€:\’m/5 at a" (O Ola i=i‘u6-fi (Magovedk [j ‘? ob ANSWER: g 3‘13 @ (c) Using your answer for speed from part a., what would be the radius of the circle if the proton entered at an angle of 35° to the magn 'c’fiéld rather than 90°? "~ Q L \ € firm/s)?" mkf:<1_s“>(\ log--\O\L\)(Sw\rb .1). k\ b€_a_*Kp\\ If End Q2. .— [4/ 3 a .__._l 3. MAGNETIC FORCES (30 Marks) (a) A straight horizontal conductor carrying a current of 35.00A from south to north passes through the magnetic field of a large magnet. The magnitude of the magnetic field is 1.60 T and its direction is vertically upward. If the field acts over a 1.50 m length of the wire, determine the magnitude and direction of the force on the wire. 6 RA i\ if) " (SS.oorDr\(\50“\<‘ 9°“ ANSWER: F: 8% N {L i /' U” .i- Direction (b) Three parallel wires each of length 2.50 m carry a different current I; = 1.00A, 12 = 3.00A and I3 = 2.00 A as shown in the figure below. The separation between adjacent wires is 2.00 cm. = 0 no 1"“ Ia (i) Calculate the total magnetic field (magnitude and direction) at point A on the TOP w' . Am. ' “D M. mw‘) L ANSWER: B=_ Em 2 RUM ’ 63:“ 1%,“ ‘ Direction {g of ya O 5 ' ‘ .. in Colt“: (ii) Calculate the magnitude and directiem of the magnetic force experienced by the TOP wire. 1w)”. ladyi . f. A}; 2 ‘/ ANSWER: F=E36—; _N 2— .‘l ’§L$(} (l/ Direction % 0 (iii) What would be the magnitude and direction of the magnetic force at point A on the top wire if you reversed the direction and doubled the current in the top wire? (9 ANSWER: F= L16 "Ll N / . End Q3. Direction dQNfl { 4. FARADAY’S LAW (15 Marks) The entire piece of copper wire of length L 2 2.52m is bent into the shape of a circle of radius r = 0.20 m. It is placed completely in a magnetic field of B = 2.00 T and oriented such that the area vector A of the loop is parallel to B. The loop is then pulled completely out of the magnetic field. It takes 1.50 milliseconds to pull the loop out. (i) Calculate the magnitude of the emf induced across the endsrof the loop. 1 ..9cum‘\\‘\ : 3 ‘qbw‘f / (V l/ j/OYVJQ, W“ ‘/ :7 NC?) I ANSWER: emf = (ii) If the same length of wire had been bent to form a single loop in the shape of an equilateral triangle and the xperiment repeated, what now would be the induced emf across the ends of the 1M \ @3 m1 ANSWER: emf = End Q4. \ [V3 End of Exam. ...
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