Electricity

Question 1

What is revers bias?

Answer 1

• voltage is large + negative

- has greatest resistance

Question 2

Diode

Answer 2

Only lets current fellow in 1 direction, unless the voltage is in the other direction = very large

Question 3

Define potential divider

Answer 3

• More than 1 resistor connected in series which can be used to split a p>d

Question 4

Explain the shape of a of an I-V filament lamp

Answer 4

• As V increases I increases
• Current heats the filament bulb (p=IV)
• Thus, increases resistance (atoms vibrate more)
• Increasing P.D causes smaller increases current as resistance also increases.

Question 5

Explain why the current of a filament bulb decreases over a period of time?

Answer 5

_ As temperature of filament increases the resistance of filament increases.

Question 6

State + explain why the filament is most likely to fail as it is switched on.

Answer 6

• Resistance of lamps will be lower when first switched on.
• Thus, lower initial current is larger
• Then a sudden change in temperature.

Question 7

State the significance of the critical temperature of a material.

Answer 7

• Below critical temperature, material becomes a superconductor.
• 0 resistance.

Question 8

When f=finding resistance of complicated circuits.

Answer 8

Add all the series to make this parallel to the other resistor.
-Then finish question

Question 9

-Between which points gives the highest reading on voltmeter.

Answer 9

Highest p.d = highest resistance

Question 10

Lamps relationships.

Answer 10

• Current through a lamp decreases as resistance increases.
• p.d across lamps reduce a voltage is shared.
• power is less

Question 11

Which lamp will be brighter?

Answer 11

• Whatever lamp has the highest resistance as p.d is greater

- link to equation p=IV

Question 12

When asked about voltage falling?

Answer 12

• Look for parallel resistors
• Bulb + thermistor are in parallel
• Gives a lower resistance than thermistor on its own
• total resistance in circuit has decreased.

Question 13

Why have these been plotted on graphs of current against potential difference rather than current [1] against electromotive force?

Answer 13

EMF is concerned with energy being put into the circuit; PD is concerned with energy used by components

Question 14

For the diode, state the value of resistance when the reverse bias is applied

Answer 14

Zero

Question 15

What is current-voltage graph look like for a thermistor?

Answer 15

Inverse of a filament bulb

Question 16

At present the highest critical temperature is -130 degrees. Give 2 examples of superconductors with C.T at room temperature would be useful.

Answer 16

Heat-free laptops

Long-lasting batteries

Question 17

The number of delocalised electrons in semiconductors

Answer 17

Increases with temperature

Question 18

What is resistance?

Answer 18

A measure of how difficult it is to get a current to flow.

Question 19

What happens to resistance of ohmic conductor if you double (v)

Answer 19

Nothing- the resistance of ohmic conductor is constant (if the physical conditions are kept constant

Question 20

What are the disadvantages of ohmic conductors?

Answer 20

• Metals have a critical temperature below (-263 degrees)

- getting things this cold is expensive + tricky

Question 21

Name 3 things resistance of a material depends on?

Answer 21

• Cross sectional area
• Length of the material
• resistivity

Question 22

What is resistivity?

Answer 22

The resistance of a material of 1m length with a 1m^2 cross-sectional area