Capicator with pushbuttons

[TsAmE]

An apparatus is designed to judge the accuracy with which humans can judge time-intervals.

Pressing a pushbutton (A) allows current to flow from a 15V supply rail, via a 15kΩ resistor into an earthed 1mF capacitor.

The capacitor voltage Vc is monitored by a voltmeter, and can be reset to zero by means of another pushbutton (B).

Neatly sketch the circuit.

At time zero, button B is pressed.
At time t = 1 button A is pressed an held down
At time t = 3 button A is released.
At time t = 5 button B is pressed again.

Sketch a graph showing how the capacitor voltage varies over the period t = 0 to 6 seconds.

(Correct answer attached).

I am not sure of a couple of things:

*If both button A and B are held down at the same time, will there be 2 currents (one flowing into the capacitor, and the other following to B's earth line, simultaneously)?
*When the current flows through the capacitor to earth, howcome the current doesnt travel past the capacitor to earth?
*At time t = 1 when button A is pressed and held down and the capacitor charges to +15V, does the voltage also travel through the line (like the electrons do), in the direction to the positive rail?

 

[ericgibbs]

An apparatus is designed to judge the accuracy with which humans can judge time-intervals.

Pressing a pushbutton (A) allows current to flow from a 15V supply rail, via a 15kΩ resistor into an earthed 1mF capacitor.

The capacitor voltage Vc is monitored by a voltmeter, and can be reset to zero by means of another pushbutton (B).

Neatly sketch the circuit.

At time zero, button B is pressed.
At time t = 1 button A is pressed an held down
At time t = 3 button A is released.
At time t = 5 button B is pressed again.

Sketch a graph showing how the capacitor voltage varies over the period t = 0 to 6 seconds.

(Correct answer attached).

I am not sure of a couple of things:

*If both button A and B are held down at the same time, will there be 2 currents (one flowing into the capacitor, and the other following to B's earth line, simultaneously)?
No, there will be only one current flowing, from the +15V line thru the 15K and thru A and B to 0V.
15V/15000= I

*When the current flows through the capacitor to earth, howcome the current doesnt travel past the capacitor to earth?
The current flows into the capacitor, so that its voltage increases towards +15V

*At time t = 1 when button A is pressed and held down and the capacitor charges to +15V, does the voltage also travel through the line (like the electrons do), in the direction to the positive rail?
Voltage does not travel thru the wiring, current flows.

hi,
There are two ways in which current flow is described.
Conventional Flow, thats current flows from positive to negative
and
Electron Flow, the electrons flow from negative to positive.

Is that 1milliFarad capacitor, they are usually marked as 1000microFarad [1000uF]

 

[TsAmE]

Oh I see, so the current doesnt spilt at the common point of the lines, as when the current travels into the capacitor, it doesnt go past it and thus doesnt get earthed?