May 2008 QP1
Q35
Q36
Q38
nOV/2008
Q10
Q24
Q27
Q32
with explanations please =)
Hello !
Q35The potential difference across a resistor is 12 V. The current in the resistor is 2.0 A.
4.0 C passes through the resistor.
What is the energy transferred and the time taken?
Ans Firstly, use the formula V=W/Q. U get then 12=W/4. Therefore W=48
Then Use the Formula Q=It. t=Q/I: t=4/2 = 2s
Q36A thermistor and another component are connected to a constant voltage supply. A voltmeter is
connected across one of the components. The temperature of the thermistor is then reduced but
no other changes are made.
In which circuit will the voltmeter reading increase?
Firstly, you should realise that a thermistor and a LDR behave almost in the same way. When the temperature increases, the resistance decreases (for thermistor) and when the light increases, the resistance decreases (for LDR). They say that the temperature is reduced, therefore resistance of the Thermistor is increased. However, we want the voltmeter reading to increase. For the voltmeter reading to increase, taking into account the increase resistance of the the thermistor, the answer has to be D. The box with the line and the straight part is called the Thermistor. Since Resistance increases, V increases also (cos R is directly proportional to V). Thus D is the only viable answer. Answer A cannot because the voltmeter reading will still be the same as the E.m.f of the battery. B cannot cos it will decrease. C cannot cos it will also decrease (B and C u measure across another component, thus if the Resistance of Thermistor increases, P.d. of it increases and the p.d. of the other component Decreases.
Q38The unknown e.m.f. E of a cell is to be determined using a potentiometer circuit. The balance
length is to be measured when the galvanometer records a null reading.
What is the correct circuit to use?
This is obviously the answer is B. For the potentiometer circuit, the new cell's positive end must be connected to the wire coming from the positive end of the Main Cell, and the Negative part of the new cell must connect to the negative part of the Main Cell. Also the galvanometer must be in the circuit directly adjacent to the new cell.
Oct/Nov 2008Q10Two spheres approach each other along the same straight line. Their speeds are u1 and u2
before collision, and v1 and v2 after collision, in the directions shown below.
Ok, firstly when u see somethign like this, you should remember the formula u1-u2=v2-v1 since they mention it is perfectly elastic.
So therefore, u would get u1-(-u2) = v2-v1
The negative is there because u2 is to the left, it is a vector so we assign a negative to it. Thus the answer is D
Q24Ok, now if you look at the diagram, the Amplitude of Y is about half the amplitude of X. Thus, the amplitude is 4. Then you see that Wave Y has more waves in a given time compared to Wave X. There are more of them. Thus it means it has a higher frequency then Wave X. Thus the only answer possible is D
Q27A small microwave receiver is moved from T towards S and receives signals of alternate maxima
and minima of intensity.
The distance between one maximum and the next is 15 mm.
What is the frequency of the microwaves?
Ok, this is an example of stationary waves being produced. Now, the distance between adjacent maximums ( antinodes) = wavelength/2
Thus 15 mm = wavelength/2
wavelength = 30mm. Then, since you are using microwaves, it is an electromagnetic wave, so you shld realise that its speed is always 3x10^8 ms-1
Thus, using formula c=freq x wavenlength, where c=3X10^8, you can find ur frequency which is C
Q32An electric power cable consists of six copper wires c surrounding a steel core s.
1.0 km of one of the copper wires has a resistance of 10 ? and 1.0 km of the steel core has a
resistance of 100 ?.
What is the approximate resistance of a 1.0 km length of the power cable?
Ok first thing you need to realise is that these wires are just like resistors in parallel. Thus you just have to use the resistors in parallel forumla : 1/R = 1/R1+ 1/R2+ 1/R3 . . . . Therefore 1/R= (1/10)x6 + 1/100
Then you find your R, which is B
Phew that was a long one. Dont worry abt Physics. Its pretty easy. Good Luck
