1) The terminal voltage of a current is observed to change when the battery supplies a current to an external resistor. What quantities are needed to calculate the change in voltage?
a) The battery's emf and its internal resistance
b) The battery's emf and the current
c) The current and the internal resistance of the battery
d) The current and the external resistance
2)For an electron beam, the following quantities are known:
Area A when beam hits a target
Beam current I
Accelerating potential difference V
Elementary charge on electron
Write an expession that gives the rate of arrival of electrons per unit area on the target based on the quantities given above.
The questions are very basic.
What level is this? And I'm not sure exactly which parts of the questions you do not understand or unable to do.
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change
= New - Old
= emf / (Rint + Rext) x Rext - emf
= emfRex/ (Rint +Rext) - emf(Rint+Rext)/(Rint+Rext)
= - emfRint/ (Rint + Rext)
= -emf/ (Rint +Rext) x Rint
= - Current x Rint
So answer is C
Total charge hitting the the area in time t: Q=I x t
Number of electrons hitting the target: Q/e = I x t / e
Rate of hitting: I x t / e / t = I / e
Rate of hitting per unit area: I / e / A = I / (eA)
I am not sure about the use of V in this question.