Semiconductor Electronics: Materials, Devices and Simple Circuits

Physics · Class 12

Simulation · Physics · Class 12

A one-way valve for current

"A one-way valve for current" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the lesson "Diode V-I characteristics" in Semiconductor Electronics: Materials, Devices and Simple Circuits. Right of zero is forward bias (p to +), left is reverse bias. The graph uses mA above the axis and µA below it, as the textbook's graph does, because the two currents differ a thousandfold. Forward bias lowers the barrier to V₀ − V and the current climbs steeply past the cut-in voltage (0.7 V Si, 0.2 V Ge). Reverse bias raises it to V₀ + V, widens the depletion layer and leaves only a µA saturation current. JEE Main asked 46 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson Diode V-I characteristics in Semiconductor Electronics: Materials, Devices and Simple Circuits. Change the values and watch what happens.

A one-way valve for currentPhysics · Class 12

In JEE Main

42 shifts analysed

46 questions from Semiconductor Electronics: Materials, Devices and Simple Circuits across the 42 JEE Main shifts Lumi has analysed (2017–2026).

See the past questions

The idea behind it

NCERT §14.6.2

  • To trace the V-I curve, a battery feeds the diode through a potentiometer (or rheostat) so the voltage can be varied. A milliammeter reads the large forward current and a microammeter the tiny reverse current.
  • Forward bias: the current stays almost zero until the voltage passes a threshold, then rises steeply (exponentially) for small further increases.
  • This threshold or cut-in voltage is about 0.2 V for a germanium diode and about 0.7 V for a silicon diode.
  • Reverse bias: the current is very small (µA) and almost constant as the voltage changes. This is the reverse saturation current.
  • At a critical reverse voltage, the breakdown voltage Vbr, the reverse current suddenly shoots up. Unless an external circuit limits it below the rated value, overheating destroys the junction; the same happens in forward bias if the current exceeds its rating.
  • General-purpose diodes are used only below breakdown, in the reverse saturation region.
  • So a diode passes current essentially one way: its forward resistance is low and its reverse resistance is high. Rectifiers exploit this.
  • Dynamic resistance: rd = ΔV/ΔI (Eq. 14.6), the ratio of a small change in voltage to the resulting small change in current.
  • Example 14.4 (silicon diode): between 10 mA at 0.7 V and 20 mA at 0.8 V, the forward resistance is rfb = 0.1 V / 10 mA = 10 Ω.
  • At V = −10 V the curve gives I = −1 µA, so the reverse resistance is rrb = 10 V / 1 µA = 1.0 × 10⁷ Ω, a million times the forward value.

Questions

3 answers

What does the "A one-way valve for current" simulation show?
Right of zero is forward bias (p to +), left is reverse bias. The graph uses mA above the axis and µA below it, as the textbook's graph does, because the two currents differ a thousandfold.
Does JEE Main ask questions from Semiconductor Electronics: Materials, Devices and Simple Circuits?
Yes. JEE Main asked 46 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Diode V-I characteristics" in Semiconductor Electronics: Materials, Devices and Simple Circuits (Class 12 Physics).

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