Section 6 - Magnetism and Electromagnetism P2

Question 1

How can you determine the direction of the magnetic field when you know the direction current is flowing?

Answer 1

Right hand rule
-you point your thumb in the direction of the current and then your fingers show the way that the magnetic field is around the wire

Question 2

What is the field around a straight, current carrying wire?

Answer 2

The field is made up if concentric circles with the wire in the centre

Question 3

What is the field around a flat circular coil?

Answer 3

There are concentric ellipses (stretched circles) of the magnetic field around the coil.
-similar to that of a bar magnet

Question 4

What is a solenoid?

Answer 4

A coil of wire

Question 5

What is the magnetic field like inside a current carrying solenoid?

Answer 5

Strong and uniform

-made stronger by adding a soft iron core

Question 6

What is the magnetic field like outside a current carrying solenoid?

Answer 6

The field is just like the one around a bar magnet

Question 7

What is an electromagnet?

Answer 7

When current is flowing the ends of the solenoid act like the north and south pole of a bar magnet

Question 8

When a current-carrying wire is put between magnetic poles, why is there a force creating on the wire causing it move?

Answer 8

Charged particles moving through a magnetic field will experience a force, as long as they’re not moving parallel to the field lines.

Question 9

What do transformer do?

Answer 9

They change the size of the voltage of an alternating current

Question 10

What two coils does a transformer have?

Answer 10

a primary and secondary, joined with an iron core

Question 11

What happens when an alternating voltage is applied across the primary coil of a transformer?

Answer 11

The magnetically soft iron core magnetises and demagnetises quickly
-this induces an alternating voltage in the secondary coil

Question 12

What is the ratio between the primary and secondary voltages the same as?

Answer 12

The ratio between the number of turns on the primary and secondary cells

Question 13

What do step-up transformers do?

Answer 13

they increase the voltage

they have more turns on the secondary coil than on the primary

Question 14

What do step-down transformers do?

Answer 14

they decrease the voltage

they have more turns on the primary coil than the secondary

Question 15

What is the transformer ratio?

Answer 15

input primary voltage/output secondary voltage

= number of turns on primary/number of turns on secondary [Vₚ / Vₛ = Nₚ / Nₛ

Question 16

What is the turns ratio?

Answer 16

The number of turns on the secondary coil divided by the number of turns on the primary coil

Question 17

What is the equation for power in transformers?

Answer 17

power = voltage x current
-transformers are nearly 100% efficient SO
POWER IN = POWER OUT
Vₚ x Iₚ = Vₛ x Iₛ

Question 18

What are used to make transmitting mains electricity more efficient?

Answer 18

step-up and step-down transformers are used when transmitting electricity across the country

Question 19

How are step-up and step-down transformers used when transmitting electricity across the country?

Answer 19

• voltage made by power stations is too low to be transmitted efficiently, so the lower the voltage the higher the current (current causes the wires to heat up)
• step-up transformer, used to boost the voltage
• step-down transformer, used at the end of its journey to reduce the voltage so its safer and more useful