required practical 3: resistance

Question 1

factors affecting a circuit:

Answer 1

the length of a wire

Question 2

how can the length of the wire being too short affect the resistance of electrical circuits?

Answer 2

R=V/I

resistance= Potential diff(V)/current(A)

Question 3

what is the equation to calculate resistance?

Answer 3

R=V/I

resistance= Potential diff(V)/current(A)

Question 4

how do we increase the length of a wire?

Answer 4

1. attach a wire to a meter using tape
2. connect wire to the rest of the circuit using 2 crocodile clips
3. we move the clips further apart to increase the length of the wire in the circuit
4. we can now measure the resistance in the circuit
5. we get a constant positive colleration graph that passes through zero meaning the resistance of the wire is directly proportional to the length

Question 5

how do we connect the wire to the rest of the circuit?

Answer 5

with 2 crocodile clips meaning the only part of the wire (between the two crocodile clips) is actually connected to the circuit

Question 6

name one problem with the graph we sometimes mistake
when the length of the wire is zero.
There is a small resistance
is this resistance a result or not?

Answer 6

the small resistance is NOT a result
the resistance should NOT be there
it’s a problem with the method
we call this zero error

Question 7

what is zero error

Answer 7

a zero error is a reading on a measuring instrument when the value should be zero
it’s a systematic error. We can not reduce it by carrying out repeats.
in the case of resistance, we need to subtract the zero error from all of our readings

Question 8

in the case of a resistance, what do we do to the zero error?

Answer 8

we subtract the zero error from all of our readings

Question 9

what is the zero error caused by?

Answer 9

equipment:
-the crocodile clip is not exactly at zero
resistance
-resistance caused by the contact between the crocodile clip and the wire
(can’t do anything about this)

Question 10

what is another issue in the resistance experiment, besides zero error?
how can we reduce this problem?

Answer 10

heating effects
if the temperature of the wire increases then the resistance will also increase
this affects our results
to reduce:
-use a low pd. This will keep the current low, reducing any heating in the wire.
-only turn on the current when taking a reading. Turn off the burdens between readings(reduces heating effects)

Question 11

what is a variable resistors symbol?

Answer 11

resistor but with arrow going diagonally from bottom left to top right
/

Question 12

what does a variable resistor contain?

Answer 12

a long piece of wire and a coil

Question 13

how can we change the length of the wire that the current runs through in a variable resistor?

Answer 13

by using the slider

Question 14

in a circuit, a variable resistor is used to control the pd across the lamp
by increasing the resistance, what happens to the lamp?

Answer 14

we can make the lamp dimmer