The time it takes for a microwave to heat up water depends on the volume of water and the wattage of the microwave. Generally, heating a cup (about 8 ounces or 240 milliliters) of water in a microwave with a standard power rating of 1000 watts will take approximately 1 to 2 minutes. However, this can vary depending on the efficiency of the microwave and the starting temperature of the water.
Regarding the final temperature of the water, it can reach its boiling point (100°C or 212°F) if you heat it long enough. Once the water reaches its boiling point, it will not get any hotter, as the additional energy from the microwave will be used to convert the water into steam instead of raising its temperature.
It is essential to exercise caution when handling heated water from the microwave, as it can cause severe burns. To avoid the risk of superheating (water getting hotter than its boiling point without boiling), it is advisable to place a microwave-safe object (e.g., a wooden stirrer or a microwave-safe teabag) in the water while heating. This provides nucleation sites for bubbles to form, preventing superheating and reducing the risk of sudden boiling when you disturb the water after heating. Always use appropriate safety precautions when working with heated liquids to avoid accidents.