Exercises of resistors 1. Calculate the resistance of a 10 m long Copper wire with diameter d = 1.0 mm.

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1 Exercises of resistors 1. Calculate the resistance of a 10 m long Copper wire with diameter d = 1.0 mm. 2. Calculate the resistances of following equipment: using 220V AC a) a 1000 W electric heater b) a 60 W light bulb 3. You have four 5 Ohm resistors in use. Show with pictures how you can build from them a) 15 Ohm b) 2.5 c) 2.0 Ohm resistances 4. A light bulb in a car has operating voltage 5.0 V and gives 6.0 W power. Calculate a) resistance of the bulb b) which size of dropping resistor it needs. Car battery s voltage is 12 V. 5. In an electrical multimeter the Ammeter resistance is 40 m and it measures range 0-1A. What size of shunt resistors should be used, when it should measure ranges a) 0-20 A b) 0-50 A 6. Calculate the total resistance between A and B Exercises of batteries 7. A car uses 2 batteries which are connected in parallel. A single battery has following characteristics: Electromotive force E = 12.6 V, charge Q = 50 Ah, internal resistance Rc = 40 m Calculate for the whole battery bank: a) Electromotive force b) Internal resistance c) charge d) terminal voltage when 100 A current is taken for the starter 8. In electric snowscooter, 4 Lithium batteries form a battery bank shown in picture. Each battery has E = 36V and Q = 150 Ah. Calculate for the whole battery bank a) the voltage E b) charge Q c) energy W

2 more... Cap citors 1. Calculate the charge of a 12 nf capacitor, when it is charged with 6.0 V battery. 2. A plate capacitor is made of two 2cm x 10 cm aluminium foil rectangles. A 0.50 mm thick paper filling is placed between foils. Calculate the capacitance of the capacitor? Dielectric coefficient of paper is A professional photo camera has a 200 μf capacitor, which is charged with 300 Volt using DC-DC transformer. Calculate the energy which is released in the flash? 4. Calculate the current in the circuit below? Calculate also the power use by the light bulb. DC circuits 5. Determine the currents I 1, I 2 and I 3 in the following DC circuit.

3 D. Magnetic force, DC motor 26. A proton (mass 1.67*10-27 kg and charge 1.60*10-19 C ) comes with a speed of 000 km/s at 90 angle into the Earth s magnetic field, (B = 50 μt). Calculate the radius of the circular orbit of the proton in the field. 27. Calculate the magnetic force due to 50 mt field on a 5 m long wire with 10 A current in it. Wire is perpendicular to the field. 28. The coil in a DC motor has 50 windings, its resistance is Ω and its cross area is 60 cm 2. Calculate a) the current b) maximum torque. Motor gets its power from 12 V battery and its static magnetic fieldi is 0.5 T. 29. Calculate the rotational frequency of the above DC motor, when it runs without load. 30. Calculate the rotational frequency, when the motor works against 12.0 Nm torque? Ans 26) 208 m 27) 2.5 N 28a) 120 A b) 36 Nm 29) n. 764 RPM 30) 509 RPM E.Calculation of magnetic field 31. Calculate the magnetic field at 10 cm distance from a wire with 200 A current. 32. Calculate the magnetic field at the end of a coil, when the coil has 120 windings, its length is 10 cm and 10 A current goes in the coil? 33. Calculate previous example, if the coil has an iron core with κ = Ans; 31) 0.40 mt 32) 15 mt 33) 18 T F. Induction and AC generator 34. In a basic mode AC generator a coil with 60 windings and cross area 2.0 dm 2, rotates at 3000 RPM in a 2.0 Tesla field. Calculate the a) frequency b) peak voltage c) effective voltage of the induced EMF 35. A coil has 8.0 cm length, 600 windings and cross are 4.0 cm 2. Calculate the inductance of the coil a) without iron core b)with an iron core ( this type of iron has magnetic permeability 1000) V battery, 6.0 Ohm light bulb and a switch are in series. a) Calculate the current in the circuit when switch is turned to ON? b) If a 2.0 Henry coil is added to the circuit, how does situation change: What is the final current then, how big is the time delay? Ans; 34a) 50 Hz b) 754 V c) 533V 35a) 2.3 mh b) 2.3 H 36a) 2.0 A b) final current is also 2.0 A, delay is about 0.33 s (time constant).

4 2 physics2_exerciseswithanswers.nb G. Electric network, transformer, 3 phase current 37. In an ideal transformer, primary current is 20 A primary voltage 220 V. Numbers of windings are 20 (primary coil) and 4 (sec.coil). Calculate current and voltage on secondary side. 38. A buiding has a pottery oven. Electricity is brought from 1km distance with a transmission wire with 0.50 Ohm resistance. In the building voltage is 220 V and power consumption 12 kw. Calculate a) power loss in the transmission line b) voltage loss in the transmission line c) transfer ratio (= power used in the house / power sent to the house from the distant center) 39. Answer previous questions a,b and c, if there is a transformer with transfrom ratio 1:20 in the building (which raises the voltage in the transmission line higher) 40. The effective voltage between phase wire and zero wire in a 3-phase system is 110 V. Calculate a) corresponding peak voltage b) calculate the effective value of the voltage between two phase wires 41. In a three phase system the loads of phase wires are 10 A, 20 A and 15 A. Calculate the current in the zero wire. 42. What is the zero wire current if the loads of phase wires are equal. Ans. 37) 100 A ja 44 V 38a) 1.5 kw b) 27 V c) n. 89 % 39a) 3.7 W b) 1.4 V c) n. 100% 40a) 141 V b) 173 V 41) 8.7 A 42) 0 A H. AC circuits (reactance, impedance, phase angle) V, 50 Hz AC power supply is in series with 80 Ohm resistor, 2.0 H coil and 6.0 μf capacitor. Calculate a) impedance b) reactance c) phase angle d) nominal power e) effective power f) reactive power 44 If we could change the frequency of the previous AC power supply, what would be the frequency, where phase angle would be zero (resonance) Ans. 43a) Ohm b) 97.8 Ohm c) 50.7 d) 383 W e) 243 W f) 296 W 44) Hz I. Electromagnetic waves 45. Calculate wave lengths for wollowing signals a) Radio Lappland 96.7 MHz

5 physics2_exerciseswithanswers.nb 3 b) GMS signal 1800 MHz c) Traffic radar 30 GHz Ans. 45a) 3.1 m b) 17 cm c) 1.0 cm

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