Flux and Gauss's law
1.[2p] Why does the flux of a point charge through a surrounding sphere not depend on the sphere's radius?
Why does the flux of a point charge through a surrounding sphere not depend on the sphere's radius?
The answer is: The field falls as one over r squared while the area grows as r squared, and the two cancel exactly
The answer is: The field falls as one over r squared while the area grows as r squared, and the two cancel exactly
The answer is: The field falls as one over r squared while the area grows as r squared, and the two cancel exactly
2.[2p] A charge of μC sits inside an irregular closed surface. What is the total electric flux out of it, in units of N m² C⁻¹?
A charge of μC sits inside an irregular closed surface. What is the total electric flux out of it, in units of N m² C⁻¹?
3.[2p] A charge outside a closed surface contributes nothing to the field at points on that surface.
A charge outside a closed surface contributes nothing to the field at points on that surface.
The answer is: False
4.[3p] A ball of radius 20 cm carries 80 nC spread uniformly through its volume. What is the field at 10 cm from the centre, in newtons per coulomb?
A ball of radius 20 cm carries 80 nC spread uniformly through its volume. What is the field at 10 cm from the centre, in newtons per coulomb?
5.[2p] Inside the material of a conductor in electrostatic equilibrium the field is zero because
Inside the material of a conductor in electrostatic equilibrium the field is zero because
The answer is: any field would keep pushing the free charges, so equilibrium would not have been reached
The answer is: any field would keep pushing the free charges, so equilibrium would not have been reached
The answer is: any field would keep pushing the free charges, so equilibrium would not have been reached
6.[3p] A charge of nC sits at the centre of a hollow conducting shell carrying a net charge of nC. What charge, in nanocoulombs, ends up on the shell's outer surface? Give the signed value.
A charge of nC sits at the centre of a hollow conducting shell carrying a net charge of nC. What charge, in nanocoulombs, ends up on the shell's outer surface? Give the signed value.
7.[3p] The bound on the exponent in Coulomb's law comes from looking for charge inside a hollow charged conductor rather than from measuring forces because
The bound on the exponent in Coulomb's law comes from looking for charge inside a hollow charged conductor rather than from measuring forces because
The answer is: the prediction is exactly zero, and zero can be tested to arbitrary precision without a calibration
The answer is: the prediction is exactly zero, and zero can be tested to arbitrary precision without a calibration
The answer is: the prediction is exactly zero, and zero can be tested to arbitrary precision without a calibration
8.[3p] For which of these does Gauss's law let you find the field without doing a vector integral?
For which of these does Gauss's law let you find the field without doing a vector integral?
Select all that apply
The answer is: A uniformly charged sphere, A very long straight charged wire, A large uniformly charged flat sheet
9.[3p] Match each situation to the field it produces.
Match each situation to the field it produces.
Isolated charged sheet
Just outside a conductor
Long line at distance r
Inside the metal of a conductor
sigma over two epsilon nought
zero
sigma over epsilon nought
lambda over two pi epsilon nought r
Show the answer
Isolated charged sheet: sigma over two epsilon nought Just outside a conductor: sigma over epsilon nought Long line at distance r: lambda over two pi epsilon nought r Inside the metal of a conductor: zero