if the voltage across the diode is less than the cut-in voltage of that particular diode .
increases
It depends how "ideal" your ideal diode is. The first approximation of an ideal diode is that it's a device that allows current to flow one way, and not the other way, while doing this with no losses. The second approximation of a diode implies the inherent 0.7V drop across the device, as well as one way current flow, but with no loss resistance. The third approximation of an ideal diode is a device which allows current to only flow one way through it, with a 0.7V loss across is, as well as a small internal resistance of a few ohms. These all vary from a real diode because these are all linear, in every sense. You can neither calculate the voltage nor the current across/through a diode. Instead, you must use the diode's characteristic curve (given on datasheet), and linearize it. You can get any amount of current to flow through the diode the CORRECT direction, by changing the voltage used. A number of microamps will take perhaps, a third of a Volt.
A diode is a semiconductor material which has p region and n region. In order to "turn on" and conduct current in the forward direction, a diode requires a certain amount of positive voltage to be applied across it. An ideal diode conducts only when the diode is forward biased, and then the voltage drop across the diode (Vd) is zero. When the ideal diode is reverse biased, no current flows. The two conditions to operate a diode are: (a) Current flow is permitted; the diode is forward biased. (b) Current flow is prohibited; the diode is reversed biased. When the polarity of the battery is such that current is allowed to flow through the diode, the diode is said to be forward-biased.
One description would be forward biased.
ratio of ac voltage applied across the diode to the ac current flowing through it
due to high voltage across the diode ie more than piv of the diode or current flows more than maximum allowed range of diode.
An LED is a diode that emits light; diodes allow current to flow only one direction. The voltage applied to the diode attempts to force current to flow in a specific direction. If the voltage polarity is reversed, and current was flowing before (so there was a small voltage drop across the diode), current will cease to flow (assuming the voltage is not too high for the diode to handle), and (almost) all the voltage will be dropped across the diode (a small leakage current may flow, which means some of the voltage will not be dropped across the diode, but this is in the milli or micro range). I would never define a diode as a "voltage controller" or "current controller". It could be either or both, from the above description.
A zener diode, in the reverse bias condition, presents a higher voltage. The current, however, is a function of the supplying circuit.
Diodes are measured in terms of resistance. The formula is as follows Rd = Vd / Id. That is Resistance of the diode = voltage across the diode to current flowing throught the diode.
The voltage across a semiconductor diode (and across the base/emitter junction of a transistor) decreases as temperature increases: the actual figure is -2mV/°C.
The amount of (forward biased) voltage across a diode is dependent on current and temperature. A typical silicon diode has a forward voltage of about 0.6V at low current and temperature. As current goes up, voltage goes up slightly, with a typical voltage being 1.4V at high current. As temperature goes up, voltage goes down slightly, but the maximum current rating also goes down.
A specific amount of current is allowed to flow through a diode. If the current passing through the diode exceeds this specific value, the diode gets heated and is likely to be damaged. Therefore, in the biasing circuit of a resistance which limits the current passing through the diode within its specific value is called Forward biased diode. ANSWER: A forward bias diode is just a diode that it is conducting in the forward direction. Positive to anode and negative to cathode