what happens to a current in a circuit if the voltage is not changed but the resistance is doubled?

The current may be more than double,as the motor may not start due to low voltage and the back EMF not created.

Then again, it may be much lower because certain things may not start up within the device.

Need more info, dudette!

I (current) = E (voltage) divided by R (Resistance).  If the resistance doubles then current halves.  b: current will also halve by the same formula (Ohm's law).  Current acts inversely with change only in resistance and the same with changes only in voltage.

a) current is one half, by ohms law, I = E/R

b) who knows? possibly about half, but it depends on the appliance. If it has a motor, the motor may not start at all, then the current will go way up. Bottom line, it will not operate normally, may not operate at all, may start to smoke and blow circuit breakers.

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The current in a circuit is inversely proportional to the resistance.  If the voltage stays the same and the resistance is changed, then the current is the voltage divided by the resistance.  In this case the resistance is doubled so the current is halved.

b.  The voltage is halved, from 220V to 110V, so the current will be halved.  But this assumes the appliance is capable of operating at the lower voltage.  Most appliances were not designed to operate at half voltage.  And things get really tricky when this happens.  For instance, a motor will no longer run at the lower voltage so it stops turning.  And then it may draw excessive current because it's no longer running.  Or in the case of a light bulb or heating element, the difference in temperature means that the filament or element has changed resistance, so the current is not half.  The light's tungsten filament has less resistance and the current will be more than half..Some newer electronic devices have a "universal" power supply, which operates at any voltage from 100V AC to 240V AC, and if this power supply has to put out the same power at the lower voltage, it will draw a higher current to compensate for the lower voltage.

What happens to a current in a circuit if the voltage is not changed but the resistance is doubled?
The answer to this is the current is halved. Remember I = E/R

In the b. your curling iron only gets 1/4 of the power.