Transcript Slide 1
Electric Field Questions from 2006 and 2007 Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. The oil drop is stationary. What is its charge? Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. • Force down is its weight. • If it is stationary then there must be an electric force up that is equal and opposite to the weight. Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. We therefore know that the charge must be negative (so it is attracted to the upper plate!) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. Magnitude of force down = mg Magnitude of force up = QE But E = V/d So magnitude of force up = QV/d Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. I mg I = I QV/d I So Q = - mgd/V Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. In a Rutherford scattering experiment, an α particle approaches a gold nucleus along the straight line joining their centres and comes momentarily to rest at point P, as shown in the diagram. The α particle then returns along its previous path. (a) The distance from the centre of the gold nucleus, to the point P is 30 fm. For the point P (i) show that the strength of the electric field associated with the charge of the nucleus is 1.3 × 1020 V m-1 (ii) calculate the magnitude of the force acting on the α particle (iii) calculate the electric potential due to the charge of the nucleus (5 marks) , Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. (b) (i) State the energy changes of the α particle during its interaction with the gold nucleus. (ii) Calculate the initial kinetic energy, in J, of the α particle, explaining your reasoning. (4 marks) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. • Two protons are 1.0 × 10 -14 m apart. Approximately how many times is the electrostatic force between them greater than the gravitational force between them? A 1023 B 1030 C 1036 D 1042 Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. • Two protons are 1.0 × 10 -14 m apart. Approximately how many times is the electrostatic force between them greater than the gravitational force between them? A 1023 B 1030 C 1036 D 1042 Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. (a) (i) Define the electric field strength, E, at a point in an electric field. (ii) State whether E is a scalar or a vector quantity. (3 marks) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. (a) (i) Define the electric field strength, E, at a point in an electric field. (ii) State whether E is a scalar or a vector quantity. (3 marks) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. (b) Point charges of + 4.0 nC and - 8.0 nC are placed 80 mm apart (i) Calculate the magnitude of the force exerted on the + 4.0 nC charge by the -8.0 nC charge. (ii) Determine the distance from the + 4.0 nC charge to the point, along the straight line between the charges, where the electric potential is zero. • (4 marks) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. (c) Point P is equidistant from the two charges. (i) Draw two arrows on the diagram at P to represent the directions and relative magnitudes of the components of the electric field at P due to each of the charges. (ii) Hence draw an arrow, labelled R, at P to represent the direction of the resultant electric field at P. (3 marks) Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved. Garfield Graphics included with kind permission from PAWS Inc. All Rights Reserved.