18.4. Electric field of a point charge
A subsection of Physics, 9702, through 18. Electric fields
Listing 10 of 13 questions
State a similarity between the gravitational field lines around a point mass and the electric field lines around a point charge. The variation with radius r of the electric field strength E due to an isolated charged sphere in a vacuum is shown in . 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 r / cm E / 105 V m–1 Use data from to: state the radius of the sphere radius = cm calculate the charge on the sphere. charge = C Using the formula for the electric potential due to an isolated point charge, determine the capacitance of the sphere in . capacitance = F
9702_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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Define electric field strength. An electron is accelerated from point A to point B by a uniform electric field, as illustrated in . A electron electric field B The distance between A and B is 12 mm. The velocity of the electron at A is 2.5 km s–1 and at B is 18 Mm s–1. Calculate the acceleration of the electron, acceleration = m s–2 the change in kinetic energy of the electron, change in kinetic energy = J the electric field strength. electric field strength = V m–1 An α-particle moves from A to B in the electric field in . Describe and explain how the change in the kinetic energy of the α-particle compares with that of the electron. Numerical values are not required.
9702_s17_qp_23
THEORY
2017
Paper 2, Variant 3
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State what is meant by electric field strength. Two point charges A and B are situated a distance 15 cm apart in a vacuum, as illustrated in . A P 15 cm x B Point P lies on the line joining the charges and is a distance x from charge A. The variation with distance x of the electric field strength E at point P is shown in . –2 –4 –6 x / cm E / 103 N C–1 By reference to the direction of the electric field, state and explain whether the charges A and B have the same, or opposite, signs. State why, although charge A is a point charge, the electric field strength between x = 3 cm and x = 7 cm does not obey an inverse-square law. Use to determine the ratio magnitude of charge A . magnitude of charge B ratio =
9702_s19_qp_41
THEORY
2019
Paper 4, Variant 1
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State what is meant by electric field strength. Two point charges A and B are situated a distance 15 cm apart in a vacuum, as illustrated in . A P 15 cm x B Point P lies on the line joining the charges and is a distance x from charge A. The variation with distance x of the electric field strength E at point P is shown in . –2 –4 –6 x / cm E / 103 N C–1 By reference to the direction of the electric field, state and explain whether the charges A and B have the same, or opposite, signs. State why, although charge A is a point charge, the electric field strength between x = 3 cm and x = 7 cm does not obey an inverse-square law. Use to determine the ratio magnitude of charge A . magnitude of charge B ratio =
9702_s19_qp_43
THEORY
2019
Paper 4, Variant 3
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An α-particle and a proton are at rest a distance 20 μm apart in a vacuum, as illustrated in . x P 20 +m proton _-particle State Coulomb’s law. The α-particle and the proton may be considered to be point charges. Calculate the electric force between the α-particle and the proton. force = N Define electric field strength. A point P is distance x from the α-particle along the line joining the α-particle to the proton (see ). The variation with distance x of the electric field strength Eα due to the α-particle alone is shown in . –100 electric field strength / V m–1 –200 –300 x / +m EP E_ The variation with distance x of the electric field strength EP due to the proton alone is also shown in . 1. Explain why the two separate electric fields have opposite signs. 2. On , sketch the variation with x of the combined electric field due to the α-particle and the proton for values of x from 4 μm to 16 μm.
9702_w13_qp_41
THEORY
2013
Paper 4, Variant 1
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An α-particle and a proton are at rest a distance 20 μm apart in a vacuum, as illustrated in . x P 20 +m proton _-particle State Coulomb’s law. The α-particle and the proton may be considered to be point charges. Calculate the electric force between the α-particle and the proton. force = N Define electric field strength. A point P is distance x from the α-particle along the line joining the α-particle to the proton (see ). The variation with distance x of the electric field strength Eα due to the α-particle alone is shown in . –100 electric field strength / V m–1 –200 –300 x / +m EP E_ The variation with distance x of the electric field strength EP due to the proton alone is also shown in . 1. Explain why the two separate electric fields have opposite signs. 2. On , sketch the variation with x of the combined electric field due to the α-particle and the proton for values of x from 4 μm to 16 μm.
9702_w13_qp_42
THEORY
2013
Paper 4, Variant 2
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Questions Discovered
13