Electricity and magnetism, Year 8: more practice

250

Hint1 A is 1000 mA.

The whyMultiply amps by 1000 to get milliamps: 0.25 × 1000 = 250 mA.

The current stops, so the magnetic field stops

HintWhat flows through the coil to make it act as a magnet?

The whyA coil's magnetic field exists only while current flows. An iron core stays magnetised only weakly and briefly, so the clips drop.

Its north and south poles swap

HintReverse the current and the ends reverse too.

The whyThe direction of the magnetic field depends on the direction of the current. Reversing the current reverses the poles.

A voltmeter

HintThe letter is the first of the quantity it measures.

The whyA voltmeter measures potential difference. It is drawn as a circle containing V.

A resistor

HintIt resists the flow of current.

The whyA resistor is a rectangle on the wire. A variable resistor is the same rectangle with an arrow through it.

So anyone can read and build the same circuit

HintThe aim is agreement between different people.

The whySymbols are international, so a diagram can be understood without words and without being redrawn to look like real parts.

No: the current is the same after the bulb as before

HintCompare ammeter readings either side of it.

The whyThe charge flows round the whole loop and is not used up. It is the energy it carries that is transferred in the bulb.

The volt (V)

HintIt is named after a scientist.

The whyPotential difference is measured in volts, with a voltmeter connected across the component.

3

HintSeries cells add together.

The whyThe voltages of cells in series add up: 1.5 V + 1.5 V = 3 V.

The same

HintEach branch gets the full push of the battery.

The whyIn a parallel circuit each branch gets the full potential difference of the battery, so each identical bulb is as bright as one on its own.