An isolated solid metal sphere of radius $$$r$$$ is given a positive charge. The potential at the surface of the sphere is $$$9.0 \times 10^{4} \mathrm{~V}$$$. At a distance of $$$3 r$$$ from the centre of electric field strength $$$=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{NC}^{-1}$$$ NIOYVW SIH $$$\perp$$$ NI ヨHYM $$$\perp$$$ ON OO NIOYVW SIHL NI ヨHYM $$$\perp$$$ ON OO the sphere, the electric field strength is $$$2.0 \times 10^{5} \mathrm{NC}^{-1}$$$. (i) Determine the electric field strength at the surface of the sphere. (ii) Show that the radius of the sphere is 5.0 cm . (iii) Calculate the charge on the sphere. charge = C

Physics

IGCSE&ALevel

CAIE

Exam No：9702_s25_qp_44 Year：2025 Question No：IGCSE&ALevelPhysics2025A20137

Answer:

Knowledge points:

18.3.1 understand that, for any point outside a spherical conductor, the charge on the sphere may be considered to act as a point charge at its centre

18.3.2 recall and use Coulomb's law in the form for the force between two point charges in free space or air

18.4.1 recall and use for the field strength of a point charge in free space or air

18.5.1 define potential at a point as the work done per unit positive charge in bringing a small test charge from infinity to the point

18.5.2 state that the field strength of the field at a point is equal to the negative of potential gradient at that point

18.5.3 use the equation for the potential in the field of a point

18.5.4 recognise the analogy between certain qualitative and quantitative aspects of electric fields and gravitational fields

19.1.1 define capacitance and the farad, as applied to both isolated conductors and to parallel plate capacitors

19.1.2 recall and use C = $\frac{Q}{V} $

19.1.3 derive, using the formula , conservation of charge and the addition of potential differences, formulae for combined capacitance for capacitors in series and in parallel

19.1.4 solve problems using the capacitance formulae for capacitors in series and in parallel

Answer:

Knowledge points:

Solution:

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