介词加关系代词在定语从句中相当于关系副词，具体等于哪个词取决于介词和关系代词的组合以及先行词的类型。以下是一些常见的组合及其对应的词：

时间

介词：in, on, at, during, before, after

关系代词：which

对应词：when, where

例句：

This is the factory in whichhe worked.

He told me the date on whichhe joined the Party.

地点

介词：in, on, at, under, above, between, among, outside, inside

关系代词：which

对应词：where

例句：

This is the book on whichthe picture is hanging.

There is a window above whichthe sun shines.

原因

介词：for

关系代词：which

对应词：why

例句：

The reason for whichhe was late was that his car broke down.

目的

介词：for

关系代词：which

对应词：that

例句：

The book for whichshe paid a lot is very interesting.

方式

介词：in, with

关系代词：which

对应词：that

例句：

She sings ina beautiful voice.

They spoke withenthusiasm.

手段

介词：by

关系代词：which

对应词：that

例句：

They traveled bycar to the countryside.

范围

介词：of

关系代词：which

对应词：that

例句：

This is a book ofmy brother's.

数量

介词：of, among, by

关系代词：which

对应词：that

例句：

There are many books ofhis.

Among these books, byhim are the ones I like best.

总结来说，介词加关系代词在定语从句中相当于关系副词，具体等于哪个词取决于介词和关系代词的组合以及先行词的类型。常见的组合包括时间、地点、原因、目的、方式、手段、范围和数量等。希望这些信息对你有所帮助。