physic ........物理

1. You cannot find the resistance of the bulb without knowing the resistance of the other resistor (the one connected in parallel with the bulb).

The current flows through the bulb is less than 1 A due to the presence of the resistor that shares part of the 1 A current.

With the given data, you could only know that the bulb resistance is not smaller than 6 ohms.
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2. Since the cell voltage is 3 volts and the voltage across R2 when the switch is closed is 2.5 volts, the voltage across the resistance R1 is (3-2) volts = 1 volt

Hence, resistance of R1 = 1/0.5 ohms = 2 ohms