18.5. Electric potential
A subsection of Physics, 9702, through 18. Electric fields
Listing 10 of 70 questions
Define electric potential at a point. Two point charges A and B are separated by a distance of 12.0 cm in a vacuum, as illustrated in . charge A P charge B 12.0 cm x The charge of A is +2.0 × 10–9 C. A point P lies on the line joining charges A and B. Its distance from charge A is x. The variation with distance x of the electric potential V at point P is shown in . –40 –30 –20 –10 V / 102 V x / cm Use to determine: the charge of B charge = C the change in electric potential when point P moves from the position where x = 9.0 cm to the position where x = 3.0 cm. change = V An α-particle moves along the line joining point charges A and B in . The α-particle moves from the position where x = 9.0 cm and just reaches the position where x = 3.0 cm. Use your answer in to calculate the speed v of the α-particle at the position where x = 9.0 cm. v = m s–1
9702_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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Define electric potential at a point. Two point charges A and B are separated by a distance of 12.0 cm in a vacuum, as illustrated in . charge A P charge B 12.0 cm x The charge of A is +2.0 × 10–9 C. A point P lies on the line joining charges A and B. Its distance from charge A is x. The variation with distance x of the electric potential V at point P is shown in . –40 –30 –20 –10 V / 102 V x / cm Use to determine: the charge of B charge = C the change in electric potential when point P moves from the position where x = 9.0 cm to the position where x = 3.0 cm. change = V An α-particle moves along the line joining point charges A and B in . The α-particle moves from the position where x = 9.0 cm and just reaches the position where x = 3.0 cm. Use your answer in to calculate the speed v of the α-particle at the position where x = 9.0 cm. v = m s–1
9702_w20_qp_43
THEORY
2020
Paper 4, Variant 3
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An electron is travelling in a straight line through a vacuum with a constant speed of 1.5 × 107 m s–1. The electron enters a uniform electric field at point A, as shown in . electron speed 1.5 × 107 m s–1 2.0 cm uniform electric field B A The electron continues to move in the same direction until it is brought to rest by the electric field at point B. Distance AB is 2.0 cm. State the direction of the electric field. Calculate the magnitude of the deceleration of the electron in the field. deceleration = m s–2 Calculate the electric field strength. electric field strength = V m–1 The electron is at point A at time t = 0. On , sketch the variation with time t of the velocity v of the electron until it reaches point B. Numerical values of v and t do not need to be shown. v t
9702_m17_qp_22
THEORY
2017
Paper 2, Variant 2
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State one similarity and one difference between the electric field lines and the gravitational field lines around an isolated positively charged metal sphere. similarity difference A positive point charge +Q is positioned at a fixed point X and an identical positive point charge is positioned at a fixed point Y, as shown in . 2.5 cm 2.5 cm 10.0 cm X A +Q +Q B Y The charges are separated in a vacuum by a distance of 10.0 cm. Points A and B are on the line XY. Point A is a distance of 2.5 cm from X and point B is a distance of 2.5 cm from Y. The electric field strength at point A is 4.1 × 10–5 V m–1. Calculate charge +Q. +Q = C On , sketch the variation of the electric field strength E with distance d from A to B, along the line AB. –5 –4 –3 –2 –1 d / cm E / 10–5 V m–1 A small positive charge is placed at A. The electric field causes this charge to move from rest along the line AB. Describe the acceleration of the charge as it moves from A to B.
9702_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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State what is represented by an electric field line. Two point charges P and Q are placed 0.120 m apart as shown in . 0.120 m P +4.0 nC Q –7.2 nC The charge of P is +4.0 nC and the charge of Q is –7.2 nC. Determine the distance from P of the point on the line joining the two charges where the electric potential is zero. distance = m State and explain, without calculation, whether the electric field strength is zero at the same point at which the electric potential is zero. An electron is positioned at point X, equidistant from both P and Q, as shown in . P Q X On , draw an arrow to represent the direction of the resultant force acting on the electron.
9702_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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An isolated conducting sphere of radius r is given a charge +Q. This charge may be assumed to act as a point charge situated at the centre of the sphere, as shown in . . shows the variation with distance x from the centre of the sphere of the potential V due to the charge +Q. State the relation between electric field and potential. V r 2r 3r 4r x +Q r Use [T Using the relation in , on sketch a graph to show the variation with distance x of the electric field E due to the charge +Q. E x r 2r 3r 4r
9702_s05_qp_4
THEORY
2005
Paper 4, Variant 0
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An isolated conducting sphere of radius r is placed in air. It is given a charge +Q. This charge may be assumed to act as a point charge situated at the centre of the sphere. Define electric field strength. State a formula for the electric field strength E at the surface of the sphere. Also, state the meaning of any other symbols used. The maximum field strength at the surface of the sphere before electrical breakdown occurs is 2.0 ×106 V m–1. The sphere has a radius r of 0.35 m. Calculate the maximum values of the charge that can be stored on the sphere, charge = ……… ……………… C the potential at the surface of the sphere. potential = ……… ……………… V Use [T Suggest the effect of the electric field on a single atom near the sphere’s surface as electrical breakdown of the air occurs.
9702_s06_qp_4
THEORY
2006
Paper 4, Variant 0
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Use Two charged points A and B are separated by a distance of 6.0 cm, as shown in . d 6.0 cm A B The variation with distance d from A of the electric field strength E along the line AB is shown in . d /cm E / kV m–1 position of A position of B An electron is emitted with negligible speed from A and travels along AB. State the relation between electric field strength E and potential V. Examiner’s Use The area below the line of the graph of represents the potential difference between A and B. Use to determine the potential difference between A and B. potential difference = …………………………. V Use your answer to to calculate the speed of the electron as it reaches point B. speed = …………………………. m s–1 Use to determine the value of d at which the electron has maximum acceleration. d = …………………… cm Without any further calculation, describe the variation with distance d of the acceleration of the electron.
9702_s07_qp_4
THEORY
2007
Paper 4, Variant 0
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Questions Discovered
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