Search results

  1. R

    Zero order hold -- Discrete control systems

    I have some questions related to how a discrete control system is designed. One method is to design the controller in the continuous time domain, arriving at a transfer function (in the s-domain). After that, a transfer function for the ADC system must be taken into consideration. I will suppose...
  2. R

    Adiabatic irreversible expansion

    This example is taken from the wikipedia page describing irreversible processes. I just want to make sure I understand correctly why the initial state can't be reached anymore. I assume the transitions to be quasi-static, but there is friction between the piston and the cylinder. If so...
  3. R

    Charge near grounded plane

    Consider the following configuration: a grounded plane (very thin and with an infinite surface) and a positive (not important) point charge above it. What does grounded really mean? Can't I assume that it is neutral and it has infinitely many positive and negative charges? Because of the...
  4. R

    Body effect for NMOS transistor

    I would like to know why the threshold voltage increases for an NMOS transistor when the voltage difference between the source and the body terminals is greater than 0. If, for example, the body terminal is connected to -1V and the source to 0V, holes from the p-substrate are attracted to this...
  5. R

    Carrier flow in BJT when saturated

    I would like to know how carriers flow in a bipolar junction transistor when working in saturation mode. Normally, electrons would flow from the emitter to the base. Then, from the base, some recombine with holes nad leave, forming the base current, and the others (the majority) diffuse in the...
  6. R

    How torque and friction cause wheel to roll

    I apologize if this question has been answered before, but I did not find the explanation that I needed. If a torque is applied to a wheel situated on a frictional surface, what forces cause the wheel to roll? I know that if P is the contact point, the static frictional force counteracts...
  7. R

    Vertical spring with one attached mass and one unattached

    If an object is attached to a spring and on top of that object another object is put (but not attached), how can the motion of the spring be described (the part that I find difficult is finding the normal force between the two objects) and when does the second object separate from the first one...
  8. R

    Vertical spring and unattached mass

    Suppose I have a vertical spring and an object. If I slowly put the object on the spring until it reaches the new equilibrium point, and then I push it more and after that I release it, when exactly will the object "separate" from the spring? Thank you.
  9. R

    Capacitor "resistance"?

    Homework Statement I was told that I can measure the "resistance" of a capacitor using 3 methods: 1. "The direct method" R = \int_1^2 \frac{\rho}{A} ds 2. "Ohm's Law" R=\frac{U}{I} U=\int_1^2 E ds E=\rho J = \frac{\rho i}{A} 3. "The analogy between electrostatics and electrokinetics"...
  10. R

    Two-port network: Image impedances

    Homework Statement If we have a two-port network, a source with impedance Zs and a load with impedance Zl, I think that the conjugate of Zg and Zl (normal, not conjugated) should be equal to the image impedances of the network. The problem is that I was told that instead of the conjugate of...
  11. R

    Electric field lines produced by two eccentric charged cylinders

    Homework Statement This is the theory for a laboratory session. If we have two hollow cylinders, one with radius r1 and the other with radius r7, the center of the first one being placed at a distance d from the center of the second one, what are the surfaces having the same electric...
Top