Electricity and Electromagnetism：练习题

Which of the following correctly describes the magnetic poles when two magnets are brought together?

A student uses a variable resistor (rheostat) in a circuit with a lamp and a battery. What happens to the brightness of the lamp and the current in the circuit if the resistance of the variable resistor is increased?

In a parallel circuit, three resistors with values of \( 6 \, \Omega \), \( 12 \, \Omega \), and \( 4 \, \Omega \) are connected across a \( 12 \text{ V} \) power supply. What is the total current leaving the power supply?

What is the standard unit of electrical resistance?

In the circuit diagram shown, three resistors are connected in series to a \( 12 \text{ V} \) battery. If the resistances are \( 2 \, \Omega \), \( 4 \, \Omega \), and \( 6 \, \Omega \) respectively, what is the total current flowing through the circuit?

A student builds a simple series circuit consisting of a 6V battery, a switch, and a 3\(\Omega\) resistor.

(a) Calculate the current flowing through the circuit when the switch is closed. (2 marks)
(b) If another identical 3\(\Omega\) resistor is added in series to the circuit, what will be the new current? (1 mark)