# 9702 June 2009 Paper 22 Worked Solutions | A-Level Physics

## Paper 22

__Question 1__**(a)**

2 of SI base quantities and their
units are mass (kg) and length (m).

3 other SI base quantities and
units:

Examples: time (s), current (A),
temperature (K), amount of substance (mol), luminous intensity (cdl)

**(b)**

Pressure p due to liquid of density
ρ is related to depth h by expression p
= ρgh, where g is acceleration of free fall. Determine derived units of
pressure:

Density ρ = mass / volume

Unit of density ρ: kg m

^{-3}
Unit of acceleration g: m s

^{-2}
Unit of pressure P: kgm

^{-3}ms^{-2}m = kgm^{-1}s^{-2}

__Question 2__**{Detailed explanations for this question is available as Solution 1015 at Physics 9702 Doubts | Help Page 211 -**

*http://physics-ref.blogspot.com/2015/10/physics-9702-doubts-help-page-211.html*}

__Question 3__**{Detailed explanations for this question is available as Solution 1091 at Physics 9702 Doubts | Help Page 232 -**

*http://physics-ref.blogspot.com/2016/01/physics-9702-doubts-help-page-232.html*}

__Question 4__
Spring having spring constant k
hangs vertically from fixed point. Load of weight L, when hung from spring,
causes extension e. Elastic limit of spring is not exceeded.

**(a)**

(i)

An elastic deformation is the change
of shape / size / length / dimension when a (deforming) force is removed,
returns to original shape / size

(ii)

Relation between k, L and e:

L = ke

**(b)**

Some identical springs, each with
spring constant k, are arranged as shown. Load on each of the arrangements is
L. For each arrangement, complete table by determining (i) total extension in
terms of e, (ii) spring constant in terms of k.

{Force, L = (spring constant, k) x( extension, e). L is constant in all cases. e can be determined from the diagrams. E.g. 2 springs in parallel causes extension to be halved while 2 springs in series causes extension to be doubled. Spring constant, k is given by k = F / extension. In this question, F is constant – so, k is the reciprocal of the extension}

{Force, L = (spring constant, k) x( extension, e). L is constant in all cases. e can be determined from the diagrams. E.g. 2 springs in parallel causes extension to be halved while 2 springs in series causes extension to be doubled. Spring constant, k is given by k = F / extension. In this question, F is constant – so, k is the reciprocal of the extension}

Arrangement 1:

Extension = 2e

Spring constant = ½ k

Arrangement 2:

Extension = ½ e

Spring constant = 2k

Arrangement 3:

Extension = (3/2) e

Spring constant = (2/3) k

__Question 5__
Double-slit interference experiment
is set up using coherent red light as illustrated. Separation of slits is 0.86 mm. Distance of
screen from double slit is 2.4 m. A series of light and dark fringes is
observed on screen.

**(a)**

Coherent light is light having a constant

__phase difference__**(b)**

Estimate separation of dark fringes
on screen:

Wavelength estimate 750nm to
550nm

Separation = λD / x = (650x10

^{-9})(2.4) / (0.86x10^{-3}) = 1.8mm**(c)**

Initially, light passing through
each slit has same intensity. Intensity of light passing through one slit now
reduced. Explain effect, if any, on dark fringes observed on screen:

There is no longer complete
destructive interference / the amplitudes no longer completely cancel. So, the
dark fringes are lighter.

__Question 6__
2 vertical parallel metal plates are
situated 2.50 cm apart in vacuum. Potential difference between plates is 350 V,
as shown. An electron is initially at rest close to negative plate and in
uniform electric field between plates.

**(a)**

(i)

Magnitude of electric field between
plates:

E = V / d = 350 / (2.5x10

^{-2}) = 1.4x10^{4}NC^{-1}
(ii)

Show that force on electron due to
electric field is 2.24x10

^{-15}N:
Force = Eq = (1.4x10

^{4}) (1.6x10^{-19}) = 2.24x10^{-15}N**(b)**

Electron accelerates horizontally
across space between plates.

(i)

Horizontal acceleration of electron:

Force, F = ma

a = (F/m =) (2.24x10

^{-15}) / (9.1x10^{-31}) = 2.46x10^{15}ms^{-2}
(ii)

Time to travel horizontal distance
2.50cm between plates:

s = ½at

^{2}
2.5x10

^{-2}= ½ (2.46x10^{15}) t^{2}
Time, t = 4.5x10

^{-9}s**(c)**

Why gravitational effects on
electron need not be taken into consideration in calculation in (b):

EITHER The gravitational force is
normal to the electric force OR The electric force is horizontal while the
gravitational force is vertical.

__Question 7__**(a)**

Network of resistors, each of
resistance R, shown. The switches S

_{1}and S_{2}may be ‘open’ or ‘closed’. Resistance, in terms of R, between points X and Y for switches in positions shown:
∞

(R + R =) 2R

([1/2R + 1/2R]

^{-1}=) R**(b)**

2 cells of e.m.f. E

_{1}and E_{2}and negligible internal resistance connected into network of resistors. Currents in network are as indicated. Use Kirchoff’s laws to state relation between:
(i)

I

_{1}, I_{2}, I_{3}and I_{4}:
I

_{1}+ I_{3}= I_{2}+ I_{4}
(ii)

E

_{1}, E_{2}, R and I_{3}in loop NKLMN:
E

_{2}– E_{1}= I_{3}R
(iii)

E

_{2}, R, I_{3}and I_{4}in loop NKQN:
E

_{2}= I_{3}R + 2I_{4}R

__Question 8__
Spontaneous and random decay of radioactive
substance involves emission of either α-radiation or β-radiation and/or γ-radiation.

**(a)**

For a spontaneous decay, the rate of
decay / activity / decay (of nucleus) is not affected by external factors /
environment / surroundings

**(b)**

Type of emission that:

(i)

Not affected by electric and
magnetic fields:

Gamma / γ

(ii)

Produces greatest density of ionization
in medium:

Alpha / α

(iii)

Does not directly result in change
in proton number of nucleus:

Gamma / γ

(iv)

Has range of energies, rather than
discrete values:

Beta / β

for question 2.c)i) why is the velocity 4.2 and not 4?

ReplyDeleteThe solution has been updated.

DeleteBoth are accepted, but 4.2 is the correct value

along with the mark scheme answers, can you please explain how to get to the answers too, please...

ReplyDeleteSpecify which questions

DeletePls explain Q3bi tqvm

ReplyDeleteExplanation has been updated

Deleteq7 part a how is the resistance infinity? cant it be zero?

ReplyDeleteWhen the switches are open, no current would flow. This means that the resistance is infinite.

DeleteIf the resistance was zero, an infinite amount of current would flow.