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Transcript
Test 3 PHY101 Name: _____________________________ Date: ______________ Total points: 50 Show detailed calculations to receive full points. Use proper units. If your work is not legible it will NOT be graded. 1. Electrostatics A. Particles of charges + 1C, 2C and -3C are placed in a line. The center one is 1 m from each of the others. +1 C +2 C 1m -3 C X-axis 1m I) (2 points) Calculate the force (magnitude + direction) of the +1C on the central charge (+2 C). II) (2 points) Calculate the force (magnitude + direction) of the -3C on the central charge (+2 C). III) (3 points) Calculate the net force (magnitude + direction) on the central charge (+2 C) due to the other two. B. (1 point) State one difference between electric forces and gravitational forces. C. (3 point) Define electric field. What is its unit? Dr. Soma Dey Page 1 PHY101 Test 3 D. (2 points) Draw the electric field due to i) a positive charge and ii) a dipole. (Remember electric field is a vector). E. (3 points) How much kinetic energy will an electron gain if it accelerates through a potential difference of 23,000 V in a TV picture tube. (charge on a electron = 1.6 x 10-19 C) 2. Electric Current A. (1 point) State Ohm’s law. B. (1 point) Does current cause voltage or voltage cause current? C. Three 1 ohm resistors are connected in series to a 6 V battery. I) (1 point)) Draw a neatly labeled circuit diagram. (Show the direction of current flow.) II) (1 point) Find the total resistance of the circuit. III) (2 point) Calculate the current flowing through each resistor. Dr. Soma Dey Page 2 PHY101 Test 3 IV) (2 point) Calculate the potential drop across each resistor. D. Three 1 ohm resistors are connected in parallel to a 6 V battery. i) (1 point) Draw a neatly labeled circuit diagram. (Show the direction of current flow.) ii) (2 point) Find the total resistance of the circuit. iii) (2 point) Calculate the current flowing through each resistor. iv) (1 point) What is the potential drop across each resistor. Dr. Soma Dey Page 3 PHY101 E. Test 3 (5 points) A car’s headlights dissipate 40 W on low beam and 50 W on high beam. If it is connected to a 12 V battery, which has more resistance. (Do not just state, show calculation to get points!!!) If it costs $ 0.15 per kWh, how much does it cost to run the headlights in low beam for 6 hours? 3. Magnetism: A. (1 point) In what way are magnetic poles different from electric poles? B. (1 point) What is the direction of the magnetic field surrounding a current carrying wire? C. (2 point) In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force? D. (1 point) What is a magnetic domain? Dr. Soma Dey Page 4 PHY101 Test 3 4. Electromagnetic induction: A. (1 point) What is electromagnetic induction? B. (2 point) State Faraday’s law? C. (3 point) What are the 3 factors on which the induced voltage depends on during electromagnetic induction? D. (5 point) A transformer has 320 turns in the primary coil and 120 in the secondary coil. i) What kind of transformer is this? ii) By what factor does it change the voltage? iii) By what factor does it change the current? (For an ideal transformer power input is equal to power output.) Formulae sheet: F = k(Q1Q2)/d2 K = 9 x 10 9 N.m2/C2 Electric field = F/Q Electric potential = electric potential energy / charge In series: R = R1 + R2 + R3 … Dr. Soma Dey In parallel: 1/R = 1/R1 + 1/R2 + 1/R3 … Current = Voltage / resistance Power = current X voltage (Primary voltage/# of turns ) = (secondary voltage/ # of turns) Page 5