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18.3. Electric force between point charges
A subsection of Physics, 9702, through 18. Electric fields
Listing 10 of 28 questions
Two solid metal spheres A and B, each of radius 1.5 cm, are situated in a vacuum. Their centres are separated by a distance of 20.0 cm, as shown in . P sphere A sphere B x 20.0 cm 1.5 cm 1.5 cm (not to scale) Both spheres are positively charged. Point P lies on the line joining the centres of the two spheres, at a distance x from the centre of sphere A. The variation with distance x of the electric field strength E at point P is shown in . –10 –20 –30 –40 –50 x / cm E / N C–1 Use to determine the ratio magnitude of charge on sphere A magnitude of charge on sphere B . Explain your working. ratio = The variation with distance x of the electric potential V at point P is shown in . 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 V / V x / cm An α-particle is initially at rest on the surface of sphere A. The α-particle moves along the line joining the centres of the two spheres. Determine, for the α-particle as it moves between the two spheres, its maximum speed, maximum speed = m s–1 its speed on reaching the surface of sphere B. speed = m s–1
9702_w16_qp_42
THEORY
2016
Paper 4, Variant 2
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State Coulomb’s law for the force between two point charges. Two point charges are situated in a vacuum and separated by a distance R. The force between the charges is FC. On , sketch a graph to show the variation of the force F between the charges with separation x for values of x from x = R to x = 4R. R 0.2 Fc 0.4 Fc 0.6 Fc F 0.8 Fc 1.0 Fc 2R 3R 4R x Two coils C and D are placed close to one another, as shown in . I coil C coil D V e.m.f. E
9702_w17_qp_41
THEORY
2017
Paper 4, Variant 1
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For any point outside a spherical conductor, the charge on the sphere may be considered to act as a point charge at its centre. By reference to electric field lines, explain this. An isolated spherical conductor has charge q, as shown in . x P sphere, charge q Point P is a movable point that, at any one time, is a distance x from the centre of the sphere. The variation with distance x of the electric potential V at point P due to the charge on the sphere is shown in . V / 103 V x / cm Use to determine the electric field strength E at point P where x = 6.0 cm, E = N C–1 the radius R of the sphere. Explain your answer. R = cm
9702_w17_qp_42
THEORY
2017
Paper 4, Variant 2
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State Coulomb’s law for the force between two point charges. Two point charges are situated in a vacuum and separated by a distance R. The force between the charges is FC. On , sketch a graph to show the variation of the force F between the charges with separation x for values of x from x = R to x = 4R. R 0.2 Fc 0.4 Fc 0.6 Fc F 0.8 Fc 1.0 Fc 2R 3R 4R x Two coils C and D are placed close to one another, as shown in . I coil C coil D V e.m.f. E
9702_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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Define electric potential. An isolated conducting sphere in a vacuum has radius r and is initially uncharged. It is then charged by friction so that it carries a final charge Q. This charge can be considered to be acting at the centre of the sphere. By considering the electric potential at its surface, show that the capacitance C of the sphere is given by C = 4πε0r where ε0 is the permittivity of free space. The dome of an electrostatic generator is a spherical conductor of radius 13 cm. It is initially charged so that the electric potential at the surface is 4.5 kV. A smaller isolated sphere of radius 5.2 cm, initially uncharged, is brought near to the dome. Sparking causes a current between the two spheres until they reach the same potential. Assume that any charge on a sphere may be considered to act as a point charge at its centre. Calculate the charge that is transferred between the two spheres. charge = C
9702_w21_qp_42
THEORY
2021
Paper 4, Variant 2
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State Coulomb’s law. shows an isolated hollow conducting sphere that is positively charged. + + + + + + + + On , draw field lines to represent the electric field outside the sphere. shows the variation of the electric field strength E with distance x from the centre of the sphere in . x / cm E / 105 N C–1 Determine the radius, in cm, of the sphere. radius = cm Calculate the charge on the sphere. charge = C Suggest an explanation for the fact that the electric field inside the sphere is zero.
9702_w24_qp_42
THEORY
2024
Paper 4, Variant 2
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Questions Discovered
28