Introduction:
In a transistor circuit, the collector current is the current flowing through the collector terminal of the transistor. The steady-state value refers to the final, stable value that the collector current reaches after a sufficient amount of time has passed. However, the collector current does not reach this steady-state value instantaneously.

Reasons for Delay:
The delay in reaching the steady-state value of the collector current is primarily due to stray capacitances in the circuit. Stray capacitances are parasitic capacitances that exist between different elements of the circuit, such as between the collector and other nearby conductive elements.

Effect of Stray Capacitances:
The presence of stray capacitances introduces a time constant into the circuit, which determines the rate at which the collector current changes. This time constant is given by the product of the stray capacitance and the total resistance in the circuit.

When a voltage step is applied to the input of the transistor circuit, the stray capacitances initially act as open circuits, preventing any current flow. As a result, the collector current remains zero, and the circuit is in transient mode.

Charging Process:
During the transient period, the stray capacitances start to charge. As the stray capacitances charge, the voltage across them gradually increases. Consequently, the voltage at the collector terminal also increases, allowing the collector current to flow.

The charging process continues until the voltage across the stray capacitances reaches a level that allows the collector current to reach its steady-state value. This charging process takes a certain amount of time, depending on the value of the stray capacitances and the resistance in the circuit.

Conclusion:
In conclusion, the collector current does not reach its steady-state value instantaneously in a transistor circuit due to the presence of stray capacitances. These stray capacitances introduce a time constant into the circuit, causing a delay in the charging process and the subsequent increase in the collector current. Understanding the effects of stray capacitances is essential for accurately analyzing transistor circuits and predicting their behavior.