The current voltage relation of diode is given by I = (e1000v/T – 1) mA, where the applied voltage V is in volts and the temperature T is in degree kelvin. If a student makes an error measuring ± 0.01 V while measuring the current of 5mA at 300K, what will be the error in the value of current in mA?
The diode current is given by I = (e1000V/T – 1) mA. We need to find the error in current, ΔI, when there is an error in voltage, ΔV = ±0.01 V, at I = 5 mA and T = 300 K.
For small changes, the error propagation is ΔI ≈ (dI/dV) * ΔV. First, find the derivative dI/dV.
dI/dV = d/dV[e1000V/T – 1] = (1000/T) * e1000V/T.
At T=300K, 1000/T = 1000/300 = 10/3. Since I = 5 mA, and I = e1000V/T – 1 ≈ e1000V/T (for I>>1mA), so e1000V/T ≈ 5.
Therefore, dI/dV ≈ (10/3) * 5 = 50/3 mA/V.
Now, ΔI ≈ (50/3) * (0.01) = 50/3 * 1/100 = 50/300 = 1/6 ≈ 0.1667 mA.
The magnitude of error is approximately 0.2 mA.
Final Answer: 0.2 mA
The given diode current-voltage relation is: mA, where V is in volts and T is in Kelvin. We are told that at T=300K, the measured current is I=5mA, and there is an error in voltage measurement of V. We need to find the resulting error in current, .
Step 1: Find the operating voltage V.
We know I=5 mA and T=300K. Let's plug these values into the diode equation to find V.
(since 5 + 1 = 6)
Taking natural logarithm (ln) on both sides:
We will use this expression for V later. The exact numerical value is not needed for the error calculation.
Step 2: Relate the error in current to the error in voltage.
The error is approximately given by the derivative of I with respect to V, multiplied by the error .
Step 3: Calculate the derivative dI/dV.
The current equation is .
Differentiating with respect to V:
From Step 1, we found that at our operating point (I=5mA, T=300K), .
Substituting T=300 and this value into the derivative:
mA/V
Step 4: Calculate the error in current.
Now we can find :
mA
Final Answer: The error in the value of the current is mA.
Error Propagation: When a quantity y depends on another quantity x (y = f(x)), the error in y () due to a small error in x () is given by . This formula is derived from the first-order Taylor series expansion and is valid for small errors.
Diode Equation: The given equation is a simplified version of the Shockley diode equation, , where is the saturation current, is the ideality factor, and is the thermal voltage (~26 mV at 300K). The constant 1000 in the exponent suggests it's a normalized form of this standard equation.