when与while的区别

①when是at
or
during
the
time
that,
既指时间点，也可指一段时间，while是during
the
time
that，只指一段时间，因此when引导的时间状语从句中的动词可以是终止性动词，也可以是延续性动词，而while从句中的动词必须是延续性动词。
②when
说明从句的动作和主句的动作可以是同时，也可以是先后发生；while
则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生。
③由when引导的时间状语从句，主句用过去进行时，从句应用一般过去时；如果从句和主句的动作同时发生，两句都用过去进行时的时候，多用while引导，如：
a.
when
the
teacher
came
in,
we
were
talking.
当此句改变主从句的位置时，则为：
while
we
were
talking,
the
teacher
came
in.
b.
they
were
singing
while
we
were
dancing.
④when和while
还可作并列连词。when表示“在那时”；while表示“而，却”，表对照关系。如：
a.
the
children
were
running
to
move
the
bag
of
rice
when
they
heard
the
sound
of
a
motor
bike.
孩子们正要跑过去搬开那袋米，这时他们听到了摩托车的声音。
b.
he
is
strong
while
his
brother
is
weak.
他长得很结实，而他弟弟却很瘦弱。
when
一般突出“突然的”意思
while
一般指同时发生的事情
例如：
i
was
playing
pc
while
he
was
looking
tv
一般用现在时
when的使用范围很广，各种情景均可使用。
while强调两个动作同时进行。
while还可表转折，这点恰恰是试题中常见的。
给个例子：i
was
doing
my
homework,while
he
was
watching
tv
in
the
sofa.
while作并列连词，意思是“而，却”，表对比
eg.
he
likes
pop
music,while
i
am
fond
of
folk
music.
when
可作并列连词，意为“那时，这时”，等于“at
that/this
time”,常用于下列句式：
①sb.
was
doing
sth.
when....
②sb.
was
about
to/going
to
do
sth.
when...
③sb.
had
just
done
sth.
when...

while引导的时间状语从句多用进行时态，而when引导的时间状语从句多用一般时态。

as和when、while的区别

while前面和后面的动作都是ing形式，如I
reading
a
book
while
my
mother
cooking
dinner。
when的前后接的形式有以下几种：
1）The
bell
rang
when
I
reading
the
book。
2）也有和while一样前后都接ing的
3）前后都接一般过去式

When
当……时候（强调一前一后）如：When
the
teacher
comes
into
the
classroom,
students
stand
up.
While
当……时候
（但是强调两者同时进行）如：
She
is
singing
while
she
is
listening
to
MP3.