For what emf does the resistor in dissipate no power? Should the emf be oriented with its positive terminal at the top or at the bottom?
and the positive terminal is bottom
We should find oriented with its positive terminal at the top or at the bottom.
When the current flows through a resistor, it dissipates energy, the rater of the dissipated energy is the power. This rate where the energy is transferred to the current to the resistor is
The dissipated power is zero when the current through the resistor is zero (no current flow). But at the condition, the current will not flow through the ? This occurs when the right battery applies a current through with the same magnitude of the left battery but in opposite direction. So, let us find the current that is flow due the left battery using Ohm's law.
Ohm's law states that the current I flows through a resistance due to the potential difference V between resistance.
So, we get the current through by using the values into equation
As we mentioned above, this is the current that flows in to make no current flows through . So, the voltage that exert this current through the resistor is calculated by Ohm's law in the form
The right battery has emf and to exerts a current in the opposite direction, its terminal positive should be bottom.
An oscillator circuit is important to many applications. A simple oscillator circuit can be built by adding a neon gas tube to an RC circuit, as shown in . Gas is normally a good insulator, and the resistance of the gas tube is essentially infinite when the light is off. This allows the capacitor to charge. When the capacitor voltage reaches a value Von, the electric field inside the tube becomes strong enough to ionize the neon gas. Visually, the tube lights with an orange glow. Electrically, the ionization of the gas provides a very-low-resistance path through the tube. The capacitor very rapidly (we can think of it as instantaneously) discharges through the tube and the capacitor voltage drops. When the capacitor voltage has dropped to a value , the electric field inside the tube becomes too weak to sustain the ionization and the neon light turns off. The capacitor then starts to charge again. The capacitor voltage oscillates between , when it starts charging, and , when the light comes on to discharge it.
a. Show that the oscillation period is
b. A neon gas tube has . What resistor value should you choose to go with a capacitor and a battery to make a oscillator?
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