IB Physics Static Electricity

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A tutorial sheet on electroscope questions is given below

  1. A radioactive sample is placed inside a charged electroscope. Describe what happens to the leaves of the electroscope.(radiation ionises the air inside the electroscope creating ions which are attracted to the leaves reducing their net charge causing them to collapse gradually).
  2. A rod is brought near the cap of a positively charged electroscope. The leaves of the electroscope collapse and then diverge as the rod comes closer to the cap. Must the rod have a net negative charge? (yes, in this case the size of the charge on the rod is much greater than the size of the charge on the electroscope).
  3. An electroscope has a net positive charge. A rod is brought near the cap of the electroscope and the leaves continually diverge as the rod approaches. Must the rod have a net positive charge? (yes).
  4. A rod is brought near the cap of a positively charged electroscope. The leaves of the electroscope diverge when the rod is near the cap. Must the rod have a net positive charge? (no).
  5. What is the test for determining the relative sign of the charge on a charged electroscope and a rod? (observe the initial effect; if the leaves collapse they are oposite in sign,if they diverge they have the same sign).
  6. A charged body at first attracts an uncharged object. True or false? (True. When a charged ebonite rod is brought near small pieces of paper a charge of unlike sign is induced on the near side of the paper attracting them to the rod. When contact is made with the rod charge of like sign is transferred to the paper repelling it from the rod).
  7. An uncharged metal disc has a radius a. A point charge q is placed on the axis of the disk at a distance d from its centre. What is the magnitude of the electric force acting on the charge q?
  8. A metal disc of radius a has a charge Q. What work was done in charging this disc?

IB Physics Harder Questions

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  1. Two parallel wires each of length 2.00 m and mass 50.0 g are supported from the same point by light insulating strings of length 1.00 m and carry equal currents of 100.0 A in opposite directions. Determine the angle between the strings. (5.18°)
  2. Two point charges of +6.00 μC and mass 50.0 g are suspended from a point by two light insulating threads of length 37.0 cm. Find the angle made by each string with the vertical when the charges are in equilibrium. (58.8°)
  3. A 1200 kg car rounds a curve of radius 70 m banked at an angle of 12°. If the car is travelling at a constant speed of 90kmh -1 , determine the magnitude of the friction force between the tyres and the road. (8035N)
  4. A bicycle and rider of total mass 75.0 kg can coast down a 4.00° hill at a constant speed of 10.0 kmh-1. At maximum exertion the cyclist can descend the hill at a speed of 30.0 kmh-1. Using the same power, at what speed can the cyclist climb this hill? Assume that the drag force on the cyclist is proportional to the square of the speed of the cyclist. (27.7 kmh-1)
  5. A ball is tied to a string of length L the other end of the string being fixed. The string is held horizontal and the ball is released from rest. A peg is located a distance 0.8L directly below the point of attachment of the string. Find the speed of the ball when it reaches the top of its circular path about the peg.
  6. Tarzan's problem. A rope of length 4.00 m hangs from a tree branch at the edge of a cliff. Tarzan runs at 10.0 ms-1 and grabs the rope at a height of 2.00 m. What is the maximum width of the valley that he can jump across? (13.6m, lets go of rope at 37.76° to the vertical). See The Physics Teacher, Jan 2014, page 6 for references.
  7. Tarzan tries again. Tarzan needs to jump across a valley of width 15.0 m. If the rope length and grab height are the same as in the previous problem, what is the least speed at which he must run if he is to reach the other side? (10.6 ms-1, lets go at 38.46° to the vertical)