CP9 Electrical components

Question 1

How can a variable resistor be used to change the current in a circuit?

Answer 1

Increasing the resistance will decrease the current

Question 2

What is the formula for the total resistance of multiple resistors in series?

Answer 2

R total = R1 + R2 + R3 …
total = 6+2 = 8Ω

Question 3

What happens to the resistance of a circuit when a resistor is added in parallel?

Answer 3

The resistance of the circuit decreases

Question 4

Describe the circuit you would use to investigate the relationship potential difference, current and resistance for a resistor

Answer 4

Build a series circuit with a power supply, a variable resistor, a resistor and an ammeter. Connect a voltmeter in parallel with the resistor.

Question 5

How would you use a circuit containing a variable resistor to make multiple measurements of potential difference and current?

Answer 5

Changing the resistance of the variable resistor will alter the values of current and p.d. which can be recorded in a table.

Question 6

If you have a graph of current against potential difference how do you find the resistance?

Answer 6

The gradient gives the resistance.

Question 7

How does current vary with potential difference in a filament lamp?

Answer 7

Initially current is proportional to p.d. the current continues to increase with p.d. but at a decreasing rate.

Question 8

Explain the shape of the I-V graph for a filament lamp

Answer 8

As the P.D. increases the current increases. As the current increases there are more collisions between electrons and metal ions in the filament causing the metal ions to vibrate more (its temperature has increased) and so the resistance of the lamp increases with current.

Question 9

How does current vary with potential difference in a diode and why?

Answer 9

0 for negative p.d. because diode only allows current to flow through in one direction

Question 10

How does current vary with potential difference in a fixed resistor?

Answer 10

directly proportional

Question 11

Increasing light intensity on an LDR …

Answer 11

…decreases the resistance of the LDR

Question 12

Increasing temperature of a thermistor…

Answer 12

…decreases the resistance of the thermistor

Question 13

Resistance causes electrical energy to be transferred to …

Answer 13

… heat / thermal energy

Question 14

Resistors get hot because …

Answer 14

… the electrons in the current collide with the ions in the lattice

Question 15

Draw the circuit symbol for a cell including representing the positive and negative terminals

Answer 15

A long line with a + and a short line with a -