Can I use a 5V adaptor on a 3v device

It could result in immediate failure that could result in smoke or even fire.

Can I use a 5V adapter to power a 4.5 V device

There is no problem while using a 5v adapter to generate a 4.5v device. A device stating 4.5v actually can generally withstand a voltage appliance of a minimum of 5.5v. Hence there is no problem applying a 5v adapter to that specific device.

Can I use 5V adapter for 9V device

In general the effect depends on the device and power supply. In general, connecting a 9V supply to 5V device could damage it immediately, or in long term, but it is impossible to say without seeing the schematics of the device how much excess voltage it can handle.

Can I use a 5V adapter to power a 6V device

The short answer is No. A 5V, 2A adapter gives 10W of power and the 6V,1A gives only 6W. That is only scraping the surface. Transistors are present in almost every electronic device today.

Can I use 5V charger for 3V battery

Probably not directly. A 5V charger has a specified voltage. If 5V are applied to a discharged Lithium-Polymer battery (around 3V), the current going into the battery might be several times over the maxium tolerable charging current for a 380mAh battery, which would be 380mA (better is 100mA).

Can I use 5V adapter for 3.7 V battery

Charging a 3.7v battery with a 5v charger. Here's everything about using a 5 V charger to charge a 3.7 V cell phone battery being safe to use: It's not safe to charge a 3.7 V cell phone battery with a 5 V charger for both the equipment and personal safety.

Can I use 5V adapter for 3.7 V

You can't just connect 5v to a lithium-ion battery and expect it to work. What will happen is the cell will reach 4.2v or fully charged, then continue to rise, much past 4.3v it will start to heat up as it cannot accept any more charge. If you carry on the cell will vent, and might even catch on fire.

Can I use a 5V adapter to power a 3.7 v device

You can't just connect 5v to a lithium-ion battery and expect it to work. What will happen is the cell will reach 4.2v or fully charged, then continue to rise, much past 4.3v it will start to heat up as it cannot accept any more charge. If you carry on the cell will vent, and might even catch on fire.

Can I use 5V adapter for 3.7 v battery

Charging a 3.7v battery with a 5v charger. Here's everything about using a 5 V charger to charge a 3.7 V cell phone battery being safe to use: It's not safe to charge a 3.7 V cell phone battery with a 5 V charger for both the equipment and personal safety.

Can I use a 5V adapter to power a 3.7 V device

You can't just connect 5v to a lithium-ion battery and expect it to work. What will happen is the cell will reach 4.2v or fully charged, then continue to rise, much past 4.3v it will start to heat up as it cannot accept any more charge. If you carry on the cell will vent, and might even catch on fire.

What would happen if A 3V appliance used A 5V battery

The electrical appliance may get warm or overheat as 5V is more than required for it to work. The bulb will not light. The bulb will be dimmer than normal.

Can I use A 5V adapter to power A 3.7 V device

In order for current to flow there needs to be a useful voltage difference. There is a voltage difference between 5 and 4.2 and 3.7. If you charged with 3.7 there would be no voltage difference, no current and no charging. Less than 4.2 volts and it won't charge fully.

Will 5V work with 3.3 V

A 3.3 V device can interface with a 5V device without any additional components. For example, a logic 1 (HIGH) from a 3.3 V device will be at least 2.4 V. This will still be interpreted as a logic 1 (HIGH) to a 5V system because it is above the VIH of 2 V.